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Document And Entity Information - USD ($) $ in Millions	12 Months Ended
Document And Entity Information - USD ($) $ in Millions	Dec. 31, 2017	Feb. 22, 2018	Jun. 30, 2017
Document Information [Line Items]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	FY
Entity Registrant Name	WESTLAKE CHEMICAL PARTNERS LP
Entity Central Index Key	0001604665
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 314.0
Common units [Member]
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		32,237,266
Subordinated units [Member]
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		0

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current assets
Cash and cash equivalents	$ 27,008	$ 88,900
Receivable under the Investment Management Agreement—Westlake Chemical Corporation (Westlake)	136,510	0
Accounts receivable, net—Westlake Chemical Corporation (Westlake)	43,884	126,977
Accounts receivable, net—third parties	18,083	12,085
Inventories	5,590	3,934
Prepaid expenses and other current assets	314	269
Total current assets	231,389	232,165
Property, plant and equipment, net	1,196,245	1,222,238
Goodwill	5,814	5,814
Deferred charges and other assets, net	81,828	95,011
Total assets	1,515,276	1,555,228
Current liabilities
Accounts payable—Westlake	14,027	12,130
Accounts payable—third parties	10,516	9,930
Accrued liabilities	15,697	15,717
Total current liabilities	40,240	37,777
Long-term debt payable to Westlake	473,960	594,629
Deferred income taxes	2,220	1,736
Other liabilities	107	123
Total liabilities	516,527	634,265
Commitments and contingencies (Note 15)
EQUITY
Accumulated other comprehensive income	279	200
Total Westlake Chemical Partners LP partners' capital	219,814	102,484
Noncontrolling interest in Westlake Chemical OpCo LP (OpCo)	778,935	818,479
Total equity	998,749	920,963
Total liabilities and equity	1,515,276	1,555,228
Limited Partner [Member] \| Common units [Member] \| Public [Member]
EQUITY
Limited partners' capital	411,228	297,367
Total equity	411,228	297,367
Limited Partner [Member] \| Common units [Member] \| Westlake [Member]
EQUITY
Limited partners' capital	50,265	4,813
Total equity	50,265	4,813
Limited Partner [Member] \| Subordinated units [Member] \| Westlake [Member]
EQUITY
Limited partners' capital	0	42,534
Total equity	0	42,534
General Partner [Member] \| Westlake [Member]
EQUITY
General partner—Westlake	(241,958)	(242,430)
Total equity	$ (241,958)	$ (242,430)

Consolidated Balance Sheets (Parenthetical) - shares	Dec. 31, 2017	Dec. 31, 2016
Common units [Member] \| Westlake [Member]
Units outstanding	14,122,230	1,436,115
Common units [Member] \| Public [Member]
Units outstanding	18,112,500	12,937,500
Subordinated units [Member] \| Westlake [Member]
Units outstanding	0	12,686,115

Consolidated and Combined Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net sales - Westlake	$ 973,081	$ 853,719	$ 834,918
Net co-products, ethylene and feedstock sales—third parties	199,900	133,017	172,303
Net sales	1,172,981	986,736	1,007,221
Cost of sales	769,314	595,405	624,339
Gross profit	403,667	391,331	382,882
Selling, general and administrative expenses	29,260	24,887	23,550
Income from operations	374,407	366,444	359,332
Other income (expense)
Interest expense—Westlake	(21,861)	(12,607)	(4,967)
Other income, net	1,792	601	160
Income before income taxes	354,338	354,438	354,525
Provision for income taxes	1,280	1,035	672
Net income	353,058	353,403	353,853
Less: Net income attributable to noncontrolling interest in OpCo	304,388	312,463	314,022
Limited partners' interest in net income subsequent to IPO	$ 48,670	$ 40,940	$ 39,831
Weighted average limited partner units outstanding (basic and diluted)
Weighted Average Number of Shares Outstanding, Basic and Diluted	28,392,470	27,059,730	27,059,730
Distributions per common unit (usd per unit)	$ 1.44	$ 1.29	$ 1.15
Common units [Member]
Other income (expense)
Limited partners' interest in net income subsequent to IPO	$ 38,010	$ 21,597	$ 21,158
Net income attributable to Westlake Chemical Partners LP subsequent to initial public offering per limited partner unit (basic and diluted)
Income per limited partner unit (usd per unit)	$ 1.72	$ 1.50	$ 1.47
Weighted average limited partner units outstanding (basic and diluted)
Weighted Average Number of Shares Outstanding, Basic and Diluted	22,101,547	14,373,615	14,373,615
Subordinated units [Member]
Other income (expense)
Limited partners' interest in net income subsequent to IPO	$ 8,994	$ 19,062	$ 18,673
Net income attributable to Westlake Chemical Partners LP subsequent to initial public offering per limited partner unit (basic and diluted)
Income per limited partner unit (usd per unit)	$ 1.43	$ 1.50	$ 1.47
Weighted average limited partner units outstanding (basic and diluted)
Weighted Average Number of Shares Outstanding, Basic and Diluted	6,290,923	12,686,115	12,686,115
Public [Member] \| Common units [Member]
Weighted average limited partner units outstanding (basic and diluted)
Weighted Average Number of Shares Outstanding, Basic and Diluted	14,270,240	12,937,500	12,937,500
Westlake [Member] \| Common units [Member]
Weighted average limited partner units outstanding (basic and diluted)
Weighted Average Number of Shares Outstanding, Basic and Diluted	7,831,307	1,436,115	1,436,115
Westlake [Member] \| Subordinated units [Member]
Weighted average limited partner units outstanding (basic and diluted)
Weighted Average Number of Shares Outstanding, Basic and Diluted	6,290,923	12,686,115	12,686,115

Consolidated Statements of Changes in Equity - USD ($) $ in Thousands	Total	Noncontrolling Interest in OpCo [Member]	Accumulated Other Comprehensive Income [Member]	Westlake [Member] General Partner [Member]	Common units [Member] Public [Member] Limited Partner [Member]	Common units [Member] Westlake [Member] Limited Partner [Member]	Subordinated units [Member] Westlake [Member] Limited Partner [Member]
Equity, beginning balance at Dec. 31, 2014	$ 834,950	$ 747,426	$ 0	$ (242,572)	$ 290,377	$ 4,038	$ 35,681
Stockholders' Equity [Roll Forward]
Net income	353,853	314,022			19,044	2,114	18,673
Net distributions to Westlake	(280)
Net effect of cash flow hedge			280
Proceeds from secondary public offering, net of finance and other offering costs	0
Quarterly distribution to unitholders	(31,074)				(14,856)	(1,650)	(14,568)
Quarterly distribution to noncontrolling interest retained in OpCo by Westlake	(310,842)	(310,842)
Equity, ending balance at Dec. 31, 2015	847,167	750,606	280	(242,572)	294,565	4,502	39,786
Stockholders' Equity [Roll Forward]
Net income	353,403	312,463		281	19,440	2,157	19,062
Net effect of cash flow hedge	(80)		(80)
Proceeds from secondary public offering, net of finance and other offering costs	0
Quarterly distribution to unitholders	(34,937)			(139)	(16,638)	(1,846)	(16,314)
Quarterly distribution to noncontrolling interest retained in OpCo by Westlake	(244,590)	(244,590)
Equity, ending balance at Dec. 31, 2016	920,963	818,479	200	(242,430)	297,367	4,813	42,534
Stockholders' Equity [Roll Forward]
Net income	353,058	304,388		1,666	23,743	9,934	13,327
Net effect of cash flow hedge	79		79
Proceeds from secondary public offering, net of finance and other offering costs	110,698				110,698
Subordinated unit conversion	0					42,352	(42,352)
Quarterly distribution to unitholders	(42,117)			(1,194)	(20,580)	(6,834)	(13,509)
Quarterly distribution to noncontrolling interest retained in OpCo by Westlake	(343,932)	(343,932)
Equity, ending balance at Dec. 31, 2017	$ 998,749	$ 778,935	$ 279	$ (241,958)	$ 411,228	$ 50,265	$ 0

Consolidated Statements of Cash Flows - USD ($)	12 Months Ended
Consolidated Statements of Cash Flows - USD ($)	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities
Net income	$ 353,058,000	$ 353,403,000	$ 353,853,000
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	113,985,000	98,210,000	81,210,000
Loss from disposition of property, plant and equipment	3,033,000	3,021,000	1,812,000
Other losses (gains), net	(1,040,000)	738,000	(286,000)
Changes in operating assets and liabilities
Accounts receivable - third parties	(6,146,000)	(552,000)	25,424,000
Net accounts receivable - Westlake	84,652,000	(90,742,000)	(11,836,000)
Inventories	(1,656,000)	(55,000)	2,755,000
Prepaid expenses and other current assets	(45,000)	(2,000)	(55,000)
Accounts payable	1,442,000	(2,175,000)	836,000
Accrued and other liabilities	(9,000)	3,791,000	2,317,000
Other, net	(9,917,000)	(77,911,000)	(3,488,000)
Net cash provided by operating activities	537,357,000	287,726,000	452,542,000
Cash flows from investing activities
Additions to property, plant and equipment	(68,858,000)	(299,638,000)	(231,185,000)
Receivable under the Investment Management Agreement—Westlake	(136,172,000)	0	0
Other	1,801,000	157,000	0
Net cash used for investing activities	(203,229,000)	(299,481,000)	(231,185,000)
Cash flows from financing activities
Proceeds from secondary public offering, net of finance and other offering costs	110,698,000	0	0
Proceeds from debt payable to Westlake	165,257,000	212,175,000	291,709,000
Repayment of debt payable to Westlake	(285,926,000)	(1,552,000)	(135,341,000)
Quarterly distributions to noncontrolling interest retained in OpCo by Westlake	(343,932,000)	(244,590,000)	(310,842,000)
Quarterly distributions to unitholders	(42,117,000)	(34,937,000)	(31,074,000)
Net cash used for financing activities	(396,020,000)	(68,904,000)	(185,548,000)
Net (decrease) increase in cash and cash equivalents	(61,892,000)	(80,659,000)	35,809,000
Cash and cash equivalents at beginning of period	88,900,000	169,559,000	133,750,000
Cash and cash equivalents at end of period	$ 27,008,000	$ 88,900,000	$ 169,559,000

Description Of Business And Significant Accounting Policies

12 Months Ended

Dec. 31, 2017

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Description Of Business And Significant Accounting Policies

Description of Business and Significant Accounting Policies

Description of Business

Westlake Chemical Partners LP ("Westlake Chemical Partners LP" or the "Partnership") is a Delaware limited partnership formed in March 2014 to operate, acquire and develop ethylene production facilities and related assets. On August 4, 2014, the Partnership completed an initial public offering (the "IPO") of 12,937,500 common units representing limited partner interests. On September 29, 2017, the Partnership completed its secondary offering of 5,175,000 common units at a price of $22.00 per unit. Net proceeds to Westlake Partners from the sale of the units was $110,739, net of underwriting discounts, structuring fees and offering expenses of approximately $3,111.

In connection with the IPO, the Partnership acquired a 10.6% interest in Westlake Chemical OpCo LP ("OpCo") and a 100% interest in Westlake Chemical OpCo GP LLC ("OpCo GP"), which is the general partner of OpCo. OpCo owns three ethylene production facilities and a common carrier ethylene pipeline (collectively, the "Contributed Assets"). On April 29, 2015, the Partnership purchased an additional 2.7% newly-issued limited partner interest in OpCo for approximately $135,341, resulting in an aggregate 13.3% limited partner interest in OpCo effective April 1, 2015. On September 29, 2017, the Partnership purchased an additional 5.0% newly-issued limited partner interest in OpCo for approximately $229,207, resulting in an aggregate 18.3% limited partner interest in OpCo, effective as of July 1, 2017. The remaining 81.7% limited partner interest in OpCo is owned by Westlake Chemical Corporation.

References in these financial statements to the Partnership, OpCo and OpCo GP used in the present tense or prospectively refer to the period subsequent to the IPO. References in these financial statements to the "Predecessor" refer to Westlake Chemical Partners LP Predecessor, the Partnership's predecessor for accounting purposes and refer to the time periods prior to the IPO. References to "Westlake" refer collectively to Westlake Chemical Corporation and its subsidiaries, other than the Partnership, OpCo and OpCo GP.

OpCo and Westlake entered into an ethylene sales agreement (the "Ethylene Sales Agreement") pursuant to which the Partnership generates a substantial majority of its revenue. For more information, see Note 2 to the consolidated financial statements.

The Partnership sells ethylene production in excess of volumes sold to Westlake, as well as all of the co-products resulting from the ethylene production, including propylene, crude butadiene, pyrolysis gasoline and hydrogen, directly to third parties on either a spot or contract basis. Co-products sold to third parties continue to be transported by rail or truck. Net proceeds (after transportation and other costs) from the sales of ethylene co-products that result from the production of ethylene purchased by Westlake are netted against the ethylene price charged to Westlake under the Ethylene Sales Agreement, thereby reducing the Partnership's exposure to fluctuations in the market prices of these co-products.

Basis of Presentation

The accompanying consolidated financial statements have been prepared in conformity with the accounting principles generally accepted in the United States.

The Partnership holds a 18.3% limited partner interest and the entire non-economic general partner interest in OpCo. The remaining 81.7% limited partner interest in OpCo is owned directly by Westlake, which has no rights to direct the activities that most significantly impact the economic performance of OpCo. As a result of the fact that substantially all of OpCo's activities are conducted on behalf of Westlake, and the fact that OpCo exhibits disproportionality of voting rights to economic interest, OpCo was deemed to be a variable interest entity. The Partnership, through its ownership of OpCo's general partner, has the power to direct the activities that most significantly impact the economic performance of OpCo, and it also has the obligation or right to absorb losses or receive benefits from OpCo that could potentially be significant to OpCo. As such, the Partnership was determined to be OpCo's primary beneficiary and therefore consolidates OpCo's results of operations and financial position. Westlake's retained interest of 81.7% is recorded as noncontrolling interest in the Partnership's consolidated financial statements.

Cash and Cash Equivalents

Cash equivalents consist of highly liquid investments that are readily convertible into cash and have a maturity of three months or less at the date of acquisition.

Allowance for Doubtful Accounts

The determination of the allowance for doubtful accounts is based on estimation of the amount of accounts receivable that the Partnership believes are unlikely to be collected. Estimating this amount requires analysis of the financial strength of the Partnership's customers, the use of historical experience, the Partnership's accounts receivable aged trial balance and specific collectability analysis. The allowance for doubtful accounts is reviewed quarterly. Past due balances over 90 days and high risk accounts, as determined by the analysis of financial strength of customers, are reviewed individually for collectability.

Inventories

Inventories primarily include product, material and supplies. Inventories are stated at the lower of cost or net realizable value. Cost is determined using the first-in, first-out ("FIFO") or average method.

Property, Plant and Equipment

Property, plant and equipment are carried at cost, net of accumulated depreciation. Cost includes expenditures for improvements and betterments that extend the useful lives of the assets and interest capitalized on significant capital projects.

Interest expense is capitalized for qualifying assets under construction. Capitalized interest costs are included in property, plant and equipment and are depreciated over the useful life of the related asset. Capitalized interest was $435, $5,961 and $5,116 for the years ended December 31, 2017, 2016 and 2015. Repair and maintenance costs are charged to operations as incurred. Gains and losses on the disposal or retirement of property, plant and equipment are reflected in the statement of operations when the assets are sold or retired.

The accounting guidance for asset retirement obligations requires the recording of liabilities equal to the fair value of asset retirement obligations and corresponding additional asset costs, when there is a legal asset retirement obligation as a result of existing or enacted law, statute or contract. The Partnership has conditional asset retirement obligations for the removal and disposal of hazardous materials from certain of the Partnership's manufacturing facilities. However, no asset retirement obligations have been recognized because the fair value of the conditional legal obligation cannot be measured due to the indeterminate settlement date of the obligation. Settlement of these conditional asset retirement obligations is not expected to have a material adverse effect on the Partnership's financial condition, results of operations or cash flows in any individual reporting period.

Depreciation is provided by utilizing the straight-line method over the estimated useful lives of the assets as follows:



Classification		Years

Buildings and improvements		40
Plant and equipment		25
Ethylene pipeline		35
Other		3-15

Impairment of Long-Lived Assets

The accounting guidance for the impairment or disposal of long-lived assets requires that the Partnership assess long-lived assets for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable, including when negative conditions such as significant current or projected operating losses exist. Other factors considered by the Partnership when determining if an impairment assessment is necessary include, but are not limited to, significant changes or projected changes in supply and demand fundamentals (which would have a negative impact on operating rates or margins), new technological developments, new competitors with significant raw material or other cost advantages, adverse changes associated with the United States and world economies and uncertainties associated with governmental actions. Long-lived assets assessed for impairment are grouped at the lowest level for which identifiable cash flows are largely independent of the cash flows of other assets and liabilities. Recoverability of assets to be held and used is measured by a comparison of the carrying amount of an asset to future net undiscounted cash flows expected to be generated by the asset. Assets are considered to be impaired if the carrying amount of an asset exceeds the future undiscounted cash flows. The impairment recognized is measured by the amount by which the carrying amount of the assets exceeds the fair value of the assets. Assets to be disposed of are reported at the lower of the carrying amount or estimated fair value less costs to sell.

Impairment of Goodwill and Intangible Assets

The accounting guidance requires that goodwill be tested for impairment at least annually, or when events or changes in circumstances indicate the fair value of a reporting unit with goodwill has been reduced below its carrying value. The impairment test for the recorded goodwill was performed in October 2017 and did not indicate impairment of the goodwill. Other intangible assets with finite lives are amortized over their estimated useful life and reviewed for impairment in accordance with the provisions of the accounting guidance. As of December 31, 2017, the Partnership's recorded goodwill was $5,814. See Note 6 for more information on the Partnership's annual goodwill impairment test.

Turnaround Costs

The Partnership accounts for turnaround costs under the deferral method. Turnarounds are the scheduled and required shutdowns of specific operating units in order to perform planned major maintenance activities. The costs related to the significant overhaul and refurbishment activities include maintenance materials, parts and direct labor costs. The costs of the turnaround are deferred when incurred at the time of the turnaround and amortized (within depreciation and amortization) on a straight-line basis until the next planned turnaround, which ranges from three to six years. Deferred turnaround costs are presented as a component of other assets, net. The cash outflows related to these costs are included in operating activities in the consolidated statement of cash flows.

Concentration of Credit Risk

Financial instruments which potentially subject the Partnership to concentration of risk consist principally of trade receivables from third-party customers who purchase ethylene and ethylene co-products. The Partnership performs periodic credit evaluations, as applicable, of the customers' financial condition and generally does not require collateral. The Partnership maintains allowances for potential losses, as applicable.

Revenue Recognition

Revenue is recognized when persuasive evidence of an arrangement exists, products are delivered to the customer, the sales price is fixed or determinable, and collectability is reasonably assured. Title and risk of loss passes to the customer upon delivery under executed customer purchase orders or contracts. Provisions for discounts, rebates and returns are provided for in the same period as the related sales are recorded.

Derivative Instruments

The accounting guidance for derivative instruments and hedging activities requires that the Partnership recognize all derivative instruments on the balance sheet at fair value, and changes in the derivative's fair value must be currently recognized in earnings or comprehensive income, depending on the designation of the derivative. If the derivative is designated as a fair value hedge, the changes in the fair value of the derivative and of the hedged item attributable to the hedged risk are recognized in earnings. If the derivative is designated as a cash flow hedge, the effective portion of the change in the fair value of the derivative is recorded in comprehensive income and is recognized in the statement of operations when the hedged item affects earnings. Ineffective portions of changes in the fair value of cash flow hedges are recognized in earnings currently.

Environmental Costs

Environmental costs relating to current operations are expensed or capitalized, as appropriate, depending on whether such costs provide future economic benefits. Remediation liabilities are recognized when the costs are considered probable and can be reasonably estimated. Measurement of liabilities is based on currently enacted laws and regulations, existing technology and undiscounted site-specific costs. Environmental liabilities in connection with properties that are sold or closed are realized upon such sale or closure, to the extent they are probable and estimable and not previously reserved. Recognition of any joint and several liabilities is based upon the Partnership's best estimate of its final pro rata share of the liability.

Income Taxes

The Partnership is a limited partnership and is treated as a partnership for U.S. federal income tax purposes and, therefore, is not liable for entity-level federal income taxes. The Partnership is, however, subject to state and local income taxes. Deferred tax expense or benefit is the result of changes in the deferred tax assets and liabilities during the period. Valuation allowances were recorded against deferred tax assets when it was considered more likely than not that the deferred tax assets will not be realized on a separate tax return basis.

Segment Reporting

The Partnership only operates one segment (ethylene production) and all of its operations are located in the United States.

Use of Estimates

The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, revenues and expenses, and the disclosure of contingent assets and liabilities. Actual results could differ from those estimates.

Other Comprehensive Income

The Partnership has not reported consolidated statements of comprehensive income for the years ended December 31, 2017, 2016 and 2015 due to immateriality of the components of other comprehensive income.

Recent Accounting Pronouncements

Revenue from Contracts with Customers (ASU No. 2014-09)

In May 2014, the Financial Accounting Standards Board ("FASB") issued an accounting standards update on a comprehensive new revenue recognition standard that will supersede the existing revenue recognition guidance. The new accounting guidance creates a framework by which an entity will allocate the transaction price to separate performance obligations and recognize revenue when each performance obligation is satisfied. Under the new standard, entities will be required to use judgment and make estimates, including identifying performance obligations in a contract, estimating the amount of variable consideration to include in the transaction price, allocating the transaction price to each separate performance obligation and determining when an entity satisfies its performance obligations. The standard allows for either "full retrospective" adoption, meaning that the standard is applied to all of the periods presented with a cumulative catch-up as of the earliest period presented, or "modified retrospective" adoption, meaning the standard is applied only to the most current period presented in the financial statements with a cumulative catch-up as of the current period. In July 2015, the FASB deferred the effective date for the revenue recognition standard. The accounting standard will now be effective for reporting periods beginning after December 15, 2017 and is not expected to have a material impact on the Partnership's consolidated financial position, results of operations and cash flows. The Partnership elected the modified retrospective method of adoption.

Leases (ASU No. 2016-02)

In February 2016, the FASB issued an accounting standards update on a new lease standard that will supersede the existing lease guidance. The standard requires a lessee to recognize assets and liabilities related to long-term leases that are classified as operating leases under current guidance on its balance sheet. An asset would be recognized related to the right to use the underlying asset and a liability would be recognized related to the obligation to make lease payments over the term of the lease. The standard also requires expanded disclosures related to leases. The accounting standard will be effective for reporting periods beginning after December 15, 2018. The Partnership is in the process of evaluating the impact that the new accounting guidance will have on its consolidated financial position, results of operations and cash flows.

Credit Losses (ASU No. 2016-13)

In June 2016, the FASB issued an accounting standards update providing new guidance for the accounting for credit losses on loans and other financial instruments. The new guidance introduces an approach based on expected losses to estimate credit losses on certain types of financial instruments. The standard also modifies the impairment model for available-for-sale debt securities and provides for a simplified accounting model for purchased financial assets with credit deterioration since their origination. The accounting standard will be effective for reporting periods beginning after December 15, 2019. The Partnership is in the process of evaluating the impact that the new accounting guidance will have on its consolidated financial position, results of operations and cash flows.

Cash Flows (ASU No. 2016-15)

In August 2016, the FASB issued an accounting standards update providing new guidance on the classification of certain cash receipts and payments including debt extinguishment costs, debt prepayment costs, settlement of zero-coupon debt instruments, contingent consideration payments, proceeds from the settlement of insurance claims and life insurance policies and distributions received from equity method investees in the statement of cash flows. This update is required to be applied using the retrospective transition method to each period presented unless it is impracticable to be applied retrospectively. In such situation, this guidance is to be applied prospectively. The accounting standard will be effective for reporting periods beginning after December 15, 2017. The adoption of the new standard is not expected to have a material impact on the Partnership's consolidated financial position, results of operations and cash flows.

Business Combinations (ASU No. 2017-01)

In January 2017, the FASB issued an accounting standard update to assist entities with evaluating when a set of transferred assets and activities is a business. The guidance requires an entity to evaluate if substantially all of the fair value of the gross assets acquired is concentrated in a single identifiable asset or a group of similar identifiable assets; if so, the set of transferred assets and activities is not a business. The guidance also requires a business to include at least one substantive process and narrows the definition of outputs by more closely aligning it with how outputs are described in ASC 606. The accounting standard will be effective for reporting periods beginning after December 15, 2017 and is not expected to have an impact on the Partnership's consolidated financial position, results of operations and cash flows.

Other Income - Gains and Losses from the Derecognition of Nonfinancial Assets (ASU No. 2017-05)

In February 2017, the FASB issued an accounting standards update to clarify the scope of guidance related to other income—gains and losses from the derecognition of nonfinancial assets, and to add guidance for partial sales of nonfinancial assets. The new guidance clarifies that an in substance nonfinancial asset is an asset or group of assets for which substantially all of the fair value consists of nonfinancial assets and the group or subsidiary is not a business. The guidance also outlines that when an entity transfers its controlling interest in a nonfinancial asset, but retains a noncontrolling interest, it will measure the retained interest at fair value resulting in full gain or loss recognition upon sale of the controlling interest. The accounting standard will be effective for reporting periods beginning after December 15, 2017 and is not expected to have an impact on the Partnership's consolidated financial position, results of operations and cash flows.

Recently Adopted Accounting Standards

Amendments to the Consolidation Analysis (ASU No. 2016-17)

In October 2016, the FASB issued an accounting standards update making certain changes to the current consolidation guidance. The amendments affect reporting entities that are required to evaluate whether they should consolidate a variable interest entity in certain situations involving entities under common control. Specifically, the amendments change the evaluation of whether a reporting entity is the primary beneficiary of a variable interest entity by changing how a reporting entity that is a single decision maker of a variable interest entity treats indirect interests in the entity held through related parties that are under common control with the reporting entity. The amendments became effective for annual periods beginning after December 15, 2016. The Partnership adopted this accounting standard effective January 1, 2017, and the adoption did not have any impact on the Partnership's consolidated financial position, results of operations and cash flow.

Initial Public Offering and Purchase of Additional Interests

12 Months Ended

Dec. 31, 2017

Equity [Abstract]

Initial Public Offering and Purchase of Additional Interests

Ethylene Sales Agreement

OpCo entered into a 12-year ethylene sales agreement with Westlake (the "Ethylene Sales Agreement"). The Ethylene Sales Agreement requires Westlake to purchase a minimum volume of ethylene each year equal to 95% of OpCo's planned ethylene production per year (the "Minimum Commitment"), subject to certain exceptions and a maximum commitment of 3.8 billion pounds per year. So long as Westlake is not in default under the Ethylene Sales Agreement, if OpCo's actual production exceeds planned production, Westlake has the option to purchase up to 95% of the excess production (the "Excess Production Option").

The fee for each pound of ethylene purchased by Westlake from OpCo up to the Minimum Commitment in any calendar year will equal:


•	the actual price OpCo pays Westlake to purchase ethane (or other feedstock, such as propane, if applicable) to produce each pound of ethylene, subject to a specified cap and a floor on the amount of feedstock that should be needed to produce each pound of ethylene; plus


•	the actual price OpCo pays Westlake to purchase natural gas to produce each pound of ethylene, subject to a specified cap and a floor on the amount of natural gas that should be needed to produce each pound of ethylene; plus


•	OpCo's estimated operating costs (including selling, general and administrative expenses), divided by OpCo's planned ethylene production for the year (in pounds); plus


•	a five-year average of OpCo's expected future maintenance capital expenditures and other turnaround expenditures, divided by OpCo's planned ethylene production capacity for the year (in pounds); less


•	the proceeds (on a per pound of ethylene basis) received by OpCo from the sale of co-products (including, but not limited to, propylene, crude butadiene, pyrolysis gasoline and hydrogen) associated with producing the ethylene purchased by Westlake; plus


•	a $0.10 per pound margin.

The fee for the Excess Production Option, if exercised, equals OpCo's estimated variable operating costs of producing the incremental ethylene, net of revenues from co-products sales plus a $0.10 per pound margin.

The estimated operating costs and the expected future maintenance capital expenditures and other turnaround expenditures will be adjusted at the end of each year, to be applicable for the fee for the next calendar year, to reflect certain changes in forecasted costs.

The result of the fee structure is that OpCo should recover the portion of its total operating costs and maintenance capital expenditures and other turnaround expenditures corresponding to the portion of OpCo's aggregate production that is purchased by Westlake. Any shortfall in recovery of such costs is recognized during the current year and is recoverable from Westlake in the subsequent year.

The Ethylene Sales Agreement has an initial term extending until December 31, 2026 and automatically renews thereafter for successive 12-month terms unless terminated.

Feedstock Supply Agreement

OpCo entered into a feedstock supply agreement with Westlake, pursuant to which Westlake agreed to sell to OpCo ethane and other feedstock in amounts sufficient for OpCo to produce the ethylene to be sold under the Ethylene Sales Agreement (the "Feedstock Supply Agreement"). The Feedstock Supply Agreement provides that OpCo may obtain feedstock from Westlake based on Westlake's total cost of purchasing and delivering the feedstock, including applicable transportation, storage and other costs. Title and risk of loss for all feedstock purchased by OpCo through the Feedstock Supply Agreement passes to OpCo upon delivery to one of three delivery points described in the Feedstock Supply Agreement.

The Feedstock Supply Agreement has an initial term extending until December 31, 2026 and automatically renews thereafter for successive 12-month terms unless terminated by either party; provided, however, that such agreement can only be renewed in the event the Ethylene Sales Agreement is renewed simultaneously. The Feedstock Supply Agreement may, in certain circumstances, terminate concurrently with the termination of the Ethylene Sales Agreement.

Services and Secondment Agreement

OpCo entered into a Services and Secondment Agreement with Westlake, pursuant to which OpCo provides Westlake with certain services required for the operation of Westlake's facilities; and Westlake provides OpCo with comprehensive operating services for OpCo's facilities, ranging from services relating to the maintenance and operations of the common facilities necessary for the operation of OpCo's units, to making available certain shared utilities such as electricity and natural gas that are necessary for the operation of OpCo's units. Westlake also seconds employees to OpCo to allow OpCo to operate its facilities. Such seconded employees will be under the control of OpCo while they work on OpCo's facilities.

The Services and Secondment Agreement has an initial 12-year term. The Services and Secondment Agreement may be renewed thereafter upon agreement of the parties and shall automatically terminate if the Ethylene Sales Agreement terminates under certain circumstances. Westlake and OpCo each can terminate the Services and Secondment Agreement under certain circumstances, including if the other party materially defaults on the performance of its obligations and such default continues for a 30-day period.

Site Lease Agreements

OpCo entered into two site lease agreements with Westlake pursuant to which Westlake leases to OpCo the real property underlying Lake Charles Olefins and Calvert City Olefins, respectively, and grants OpCo rights to access and use certain other portions of Westlake's ethylene production facilities that are necessary to operate OpCo's production facilities. OpCo owes Westlake one dollar per site per year. The site lease agreements each have a term of 50 years. Each of the site lease agreements may be renewed if agreed by the parties.

Omnibus Agreement

The Partnership entered into an Omnibus Agreement with Westlake that addresses (1) Westlake's indemnification of the Partnership for certain matters, including environmental and tax matters, (2) the provision by Westlake of certain management and other general and administrative services to the Partnership and its general partner and (3) the Partnership's reimbursement to Westlake for such services. The Omnibus Agreement also addresses Westlake's right of first refusal on any proposed transfer of the ethylene production facilities that serve Westlake's other facilities and Westlake's right of first refusal on any proposed transfer of the Partnership's equity interests in OpCo.

Exchange Agreement

OpCo and Westlake entered into an exchange agreement, which had an initial term through August 1, 2015 and is continuing year to year thereafter, unless and until terminated by either party. Under the exchange agreement, OpCo may require Westlake to deliver up to 200 million pounds of ethylene for OpCo per year from the Site Leases to an ethylene hub in Mt. Belvieu, Texas, for which OpCo would be required to pay an exchange fee of $0.006 per pound.

OpCo Partnership Agreement

The Partnership, OpCo GP and Westlake entered into an agreement of limited partnership for OpCo (the "OpCo LP Agreement"). The OpCo LP Agreement governs the ownership and management of OpCo and designates OpCo GP as the general partner of OpCo. OpCo GP generally has complete authority to manage OpCo's business and affairs. The Partnership controls OpCo GP, as its sole member, subject to certain approval rights held by Westlake.

Investment Management Agreement

On August 1, 2017, the Partnership, OpCo and Westlake executed the Investment Management Agreement that authorized Westlake to invest the Partnership and OpCo’s excess cash with Westlake for a term of up to a maximum of nine months. Per the terms of the Investment Management Agreement, the Partnership earns a market return plus five basis points and Westlake provides daily availability of the invested cash to meet any liquidity needs of the Partnership or OpCo. The Partnership had $136.2 million of invested cash under the Investment Management Agreement at December 31, 2017.

Accounts Receivable—Third Parties

12 Months Ended

Dec. 31, 2017

Accounts Receivable, Net [Abstract]

Accounts Receivable—Third Parties

Accounts receivable—third parties consist of the following:



	December 31,
	2017			2016
Trade customers	$	18,794		$	11,913
Allowance for doubtful accounts	(711		)	(564		)
	18,083			11,349
Other	—			736
Accounts receivable, net—third parties	$	18,083		$	12,085

- Definition

The entire disclosure for claims held for amounts due a entity, excluding financing receivables. Examples include, but are not limited to, trade accounts receivables, notes receivables, loans receivables. Includes disclosure for allowance for credit losses.

+ References + Details

Inventories

12 Months Ended

Dec. 31, 2017

Inventory, Net [Abstract]

Inventories

Inventories consist of the following:



	December 31,
	2017		2016
Finished products	$	5,244	$	3,610
Feedstock, additives and chemicals	346		324
Inventories	$	5,590	$	3,934

Property, Plant And Equipment

12 Months Ended

Dec. 31, 2017

Property, Plant and Equipment, Net [Abstract]

Property, Plant And Equipment

Property, Plant and Equipment

Property, plant and equipment consist of the following:



	December 31,
	2017			2016
Building and improvements	$	17,174		$	16,757
Plant and equipment	1,773,070			1,690,317
Other	83,167			72,215
	1,873,411			1,779,289
Less: Accumulated depreciation	(716,299		)	(644,070		)
	1,157,112			1,135,219
Construction in progress	39,133			87,019
Property, plant and equipment, net	$	1,196,245		$	1,222,238

Depreciation expense on property, plant and equipment of $91,154, $77,444 and $64,369 is included in cost of sales in the consolidated statements of operations for the years ended December 31, 2017, 2016 and 2015, respectively.

Goodwill, Deferred Charges and Other Assets

12 Months Ended

Dec. 31, 2017

Other Assets [Abstract]

Goodwill, Deferred Charges and Other Assets

Goodwill

The Partnership's goodwill balance was $5,814 at December 31, 2017 and 2016. The impairment test for the recorded goodwill was performed in October 2017 and did not indicate impairment of the goodwill. The fair value of the goodwill was calculated using both a discounted cash flow methodology and a market value methodology. The discounted cash flow projections were based on a nine-year forecast, from 2018 to 2026, to reflect the cyclicality of the Partnership's business. The forecast was based on prices and spreads projected by IHS Markit, a chemical industry organization offering market and business advisory services for the chemical market, for the same period, and estimates by management, including their strategic and operational plans. Other significant assumptions used in the discounted cash flow projection included sales volumes based on production capacities. The future cash flows were discounted to present value using a discount rate of 8.3%. The significant assumptions used in determining the fair value of the reporting unit using the market value methodology include the determination of appropriate market comparables and the estimated multiples of EBITDA a willing buyer is likely to pay.

Deferred Charges and Other Assets

Deferred charges and other assets, net consist of the following:



	Year Ended December 31,
	2017		2016
Interest rate contract	$	302	$	290
Turnaround costs, net	76,593		89,185
Other	4,933		5,536
Total deferred charges and other assets	$	81,828	$	95,011

Amortization expense on other assets of $22,831, $20,766 and $16,841 is included in the consolidated statements of operations for the years ended December 31, 2017, 2016 and 2015, respectively. Certain other assets are amortized over periods ranging from five to 15 years using the straight-line method.

Long-Term Debt

12 Months Ended

Dec. 31, 2017

Debt Disclosure [Abstract]

Long-Term Debt

Long-term debt consists of the following:



	December 31,
	2017		2016
August 2013 Promissory Notes (variable interest rate of prime plus 1.5%, original scheduled maturity of August 1, 2023)	$	—	$	31,775
OpCo Revolver (variable interest rate of London Interbank Offered Rate ("LIBOR") plus 3.0%, original scheduled maturity of August 4, 2019)	220,416		427,513
MLP Revolver (variable interest rate of LIBOR plus 2.0%, original scheduled maturity of April 29, 2021)	253,544		135,341
Long-term debt payable to Westlake	$	473,960	$	594,629

In 2013, the August 2013 Promissory Notes were issued for capital expenditures incurred by Westlake. In connection with the IPO, OpCo assumed the August 2013 Promissory Notes and used proceeds from the IPO to repay a portion of the balance it assumed. On September 29, 2017, the Partnership repaid the remaining balance of the August 2013 Promissory Notes.

In connection with the IPO on August 4, 2014, OpCo entered into a $600,000 senior unsecured revolving credit facility agreement with Westlake (the "OpCo Revolver"). The OpCo Revolver accrues interest quarterly at a rate of LIBOR plus 3.0%, which may be paid-in-kind as an addition to the principal at OpCo's option. Proceeds drawn under the OpCo Revolver during 2016 were used to fund capital expenditures at OpCo's ethylene plants and to fund the working capital requirements.

On April 29, 2015, the Partnership entered into a $300,000 revolving credit facility agreement with Westlake (the "MLP Revolver") to fund the Partnership's purchase of an additional 2.7% newly-issued, limited partner interest in OpCo for $135,341. On August 1, 2017, the Partnership entered into an amendment to the MLP Revolver agreement, extending the maturity date from April 29, 2018 to April 29, 2021. On December 5, 2017, the Partnership entered into an amendment to the MLP Revolver credit agreement, increasing borrowing capacity from $300,000 to $600,000. Borrowings under the MLP Revolver bear interest at LIBOR plus a spread ranging from 2.0% to 3.0% (depending on the Partnership's consolidated leverage ratio), payable quarterly. The MLP Revolver provides that the Partnership may pay all or a portion of the interest on any borrowings in kind, in which case any such amounts would be added to the principal amount of the loan. The MLP Revolver requires that the Partnership maintain a consolidated leverage ratio of either (1) during any one-year period following certain types of acquisitions (including acquisitions of additional interests in OpCo), 5.50:1.00 or less, or (2) during any other period, 4.50:1.00 or less. The MLP Revolver also contains certain other customary covenants. The repayment of borrowings under the MLP Revolver is subject to acceleration upon the occurrence of an event of default. During August 2015, the Partnership entered into an interest rate contract with Westlake to fix the LIBOR component of the interest rate for a portion of the MLP Revolver balance. The interest rate contract terminates on the earlier of the MLP Revolver maturity date or in August 2018.

As of December 31, 2017, the Partnership was in compliance with all of the covenants under the OpCo Revolver and the MLP Revolver.

The weighted average interest rate on all long-term debt was 3.76% and 3.72% at December 31, 2017 and 2016, respectively.

As of December 31, 2017, the Partnership had no scheduled maturities of long-term debt until 2019. The OpCo Revolver is scheduled to mature on August 4, 2019 and the MLP Revolver is scheduled to mature on April 29, 2021.

Distributions and Net Income Per Limited Partner Unit

12 Months Ended

Dec. 31, 2017

Earnings Per Share [Abstract]

Net Income Per Limited Partner Unit

8. Distributions and Net Income Per Limited Partner Unit

On January 29, 2018, the board of directors of Westlake Chemical Partners GP LLC ("Westlake GP"), the Partnership's general partner, declared a quarterly cash distribution for the period from October 1, 2017 to December 31, 2017 of $0.3864 per unit, and of $614 to the holders of the Partnership's incentive distribution rights ("IDR Holders"). This distribution was paid on February 23, 2018 to unitholders of record on February 8, 2018.

The Partnership Agreement provides that the Partnership will distribute cash each quarter during the subordination period in the following manner: first, to all the unitholders, until each unit has received the minimum quarterly distribution of $0.2750, plus any arrearages from prior quarters; and second, to all the unitholders, pro rata, until each unit has received a distribution of $0.3163. If cash distributions to the Partnership's unitholders exceed $0.3163 per unit in any quarter, the Partnership's unitholders and Westlake, as the holder of the Partnership's incentive distribution rights, will receive distributions according to the following percentage allocations:



	Marginal Percentage Interest in Distributions
Total Quarterly Distribution Per Unit	Unitholders		IDR Holders
Above $0.3163 up to $0.3438	85.0	%	15.0	%
Above $0.3438 up to $0.4125	75.0	%	25.0	%
Above $0.4125	50.0	%	50.0	%

For the three months ended December 31, 2017, the Partnership's distribution exceeded the $0.3163 per common unit target, which resulted in distributions to the IDR Holder.

The distributions are declared subsequent to quarter end; therefore, the table below represents total cash distributions declared from earnings of the related periods pertaining to such distributions.



	Year Ended December 31
	2017		2016		2015
Net income attributable to the Partnership	$	48,670	$	40,940	$	39,831
Less:
Limited partners' distribution declared on common units	34,909		19,016		16,980
Limited partners' distribution declared on subordinated units	9,133		16,784		14,986
Distributions declared with respect to the incentive distribution rights	1,666		281		—
Net income in excess of distribution	$	2,962	$	4,859	$	7,865

Net income per unit applicable to common limited partner units and to subordinated limited partner units is computed by dividing the respective limited partners' interest in net income by the weighted-average number of common units and subordinated units outstanding for the period. Because the Partnership has more than one class of participating securities, it uses the two-class method when calculating the net income per unit applicable to limited partners. The classes of participating securities include common units, subordinated units and incentive distribution rights. Net income attributable to the Partnership is allocated to the unitholders in accordance with their respective ownership percentages in preparation of the consolidated statements of changes in equity. However, when distributions related to the incentive distribution rights are made, net income equal to the amount of those distributions is first allocated to the general partner before the remaining net income is allocated to the unitholders based on their respective ownership percentages. Basic and diluted net income per unit is the same because the Partnership does not have any potentially dilutive units outstanding for the periods presented.

As discussed further in Note 9, the 12,686,115 subordinated units, all of which were owned by Westlake, were converted into common units effective August 30, 2017. For purposes of calculating net income per unit, the subordinated units were treated as if they had been converted to common units on July 1, 2017. Therefore, the subordinated units did not share in the distribution of cash generated from July 1, 2017 to December 31, 2017, and the Partnership did not allocate any earnings to the subordinated unitholders from July 1, 2017 to December 31, 2017 for the determination of net income per unit.



	December 31, 2017
	Limited Partners' Common Units		Limited Partners' Subordinated Units			Incentive Distribution Rights		Total
Net income attributable to the Partnership:
Distribution	$	34,909	$	9,133		$	1,666	$	45,708
Net income in excess of distribution (distribution in excess of net income)	3,101		(139		)	—		2,962
Net income	$	38,010	$	8,994		$	1,666	$	48,670
Weighted average units outstanding:
Basic and diluted	22,101,547		6,290,923					28,392,470
Net income per limited partner unit:
Basic and diluted	$	1.72	$	1.43



	December 31, 2016
	Limited Partners' Common Units		Limited Partners' Subordinated Units		Incentive Distribution Rights		Total
Net income attributable to the Partnership:
Distribution	$	19,016	$	16,784	$	281	$	36,081
Net income in excess of distribution	2,581		2,278		—		4,859
Net income	$	21,597	$	19,062	$	281	$	40,940
Weighted average units outstanding:
Basic and diluted	14,373,615		12,686,115				27,059,730
Net income per limited partner unit:
Basic and diluted	$	1.50	$	1.50



	December 31, 2015
	Limited Partners' Common Units		Limited Partners' Subordinated Units		Incentive Distribution Rights		Total
Net income attributable to the Partnership:
Distribution	$	16,980	$	14,986	$	—	$	31,966
Net income in excess of distribution	4,178		3,687		—		7,865
Net income	$	21,158	$	18,673	$	—	$	39,831
Weighted average units outstanding:
Basic and diluted	14,373,615		12,686,115				27,059,730
Net income per limited partner unit:
Basic and diluted	$	1.47	$	1.47

Related Party Transactions

12 Months Ended

Dec. 31, 2017

Related Party Transactions

The Partnership and OpCo regularly enter into related party transactions with Westlake. See below for a description of transactions with related parties.

Sales to Related Parties

OpCo sells ethylene to Westlake under the Ethylene Sales Agreement. Additionally, the Partnership and OpCo from time to time provide other services or products for which it charges Westlake a fee.

Sales to related parties were as follows:



	Year Ended December 31,
	2017		2016		2015
Net sales—Westlake	$	973,081	$	853,719	$	834,918

Under the Services and Secondment Agreement, OpCo uses a portion of its production capacity to process purge gas for Westlake. On August 4, 2016, OpCo and Westlake entered into an amendment to the Ethylene Sales Agreement in order to provide that certain of the pricing components that make up the price for ethylene sold thereunder would be modified to reflect the portion of OpCo's production capacity that is used to process Westlake's purge gas instead of producing ethylene and to clarify that costs specific to the processing of Westlake's purge gas would be recovered under the Services and Secondment Agreement, and not the Ethylene Sales Agreement.

Cost of Sales from Related Parties

Charges for goods and services purchased by the Partnership and OpCo from Westlake and included in cost of sales relate primarily to feedstock purchased under the Feedstock Supply Agreement and services provided under the Services and Secondment Agreement.

Charges from related parties in cost of sales were as follows:



	Year Ended December 31,
	2017		2016		2015
Feedstock purchased from Westlake and included in cost of sales	$	425,255	$	287,778	$	307,582
Other charges from Westlake and included in cost of sales	96,813		85,872		74,050
Total	$	522,068	$	373,650	$	381,632

Services from Related Parties Included in Selling, General and Administrative Expenses

Charges for services purchased by the Partnership from Westlake and included in selling, general and administrative expenses primarily relate to services Westlake performs on behalf of the Partnership under the Omnibus Agreement, including the Partnership's finance, legal, information technology, human resources, communication, ethics and compliance and other administrative functions.

Charges from related parties included within selling, general and administrative expenses were as follows:



	Year Ended December 31,
	2017		2016		2015
Services received from Westlake and included in selling, general and administrative expenses	$	27,262	$	21,971	$	20,681

Goods and Services from Related Parties Capitalized as Assets

Charges for goods and services purchased by the Partnership and OpCo from Westlake which were capitalized as assets relate primarily to the services of Westlake employees under the Services and Secondment Agreement.

Charges from related parties for goods and services capitalized as assets were as follows:



	Year Ended December 31,
	2017		2016		2015
Goods and services purchased from Westlake and capitalized as assets	$	3,491	$	17,874	$	4,332

Receivable under the Investment Management Agreement

On August 1, 2017, the Partnership, OpCo and Westlake executed an investment management agreement (the "Investment Management Agreement") that authorized Westlake to invest the Partnership and OpCo’s excess cash with Westlake for a term of up to a maximum of nine months. Per the terms of the Investment Management Agreement, the Partnership earns a market return plus five basis points and Westlake provides daily availability of the invested cash to meet any liquidity needs of the Partnership or OpCo. Accrued interest of $340 was included in the receivable under the Investment Management Agreement balance at December 31, 2017.

The Partnership's receivable under the Investment Management Agreement was as follows:



	December 31,
	2017		2016
Receivable under the Investment Management Agreement	$	136,510	$	—

Accounts Receivables

The Partnership's accounts receivable from Westlake result primarily from ethylene sales to Westlake, the shortfall recoverable from Westlake and a buyer deficiency fee, in each case under the Ethylene Sales Agreement. Under the Ethylene Sales Agreement, if production costs billed to Westlake on an annual basis are less than 95% of the actual production costs incurred by OpCo during the year, OpCo is entitled to recover the shortfall in the subsequent year. The shortfall is recognized in the period when such production activities occur. The shortfall of $63.5 million recognized in 2016 was recovered during 2017, per the Ethylene Sales Agreement. During 2016, Calvert City Olefins experienced a shutdown caused by a mechanical failure, which resulted in a force majeure event under the Ethylene Sales Agreement with Westlake. Based on the annual year-end measurement, a buyer deficiency fee of $13,106 was recognized as a receivable from Westlake and as a component of net sales in the consolidated financial statements as of and for the year ended December 31, 2016. The buyer deficiency fee was collected from Westlake in January 2017.

The Partnership's accounts payable to Westlake result primarily from feedstock purchases under the Feedstock Supply Agreement and services provided under the Services and Secondment Agreement and the Omnibus Agreement. The Partnership's accounts receivable from Westlake were as follows:



	December 31,
	2017		2016
Accounts receivable—Westlake	$	43,884	$	126,977

Accounts Payable

The Partnership's accounts payable to Westlake were as follows:



	December 31,
	2017		2016
Accounts payable—Westlake	$	14,027	$	12,130

Debt Payable to Related Parties

See Note 7 for a description of related party debt payable balances. Interest on related party debt payable balances, net of capitalized interest, for the years ended December 31, 2017, 2016 and 2015 was $21,861, $12,607 and $4,967, respectively, and is reflected as a component of other income (expense) in the consolidated and statements of operations. Interest capitalized as a component of property, plant and equipment on related party debt was $435 and $5,961 for the years ended December 31, 2017 and 2016, respectively. At December 31, 2017 and 2016, accrued interest on related party debt was $4,590 and $5,517, respectively, and is reflected as a component of accrued liabilities in the consolidated balance sheets.

Debt payable to related parties was as follows:



	December 31,
	2017		2016
Long-term debt payable to Westlake	$	473,960	$	594,629

Major Customer and Concentration of Credit Risk

During the years ended December 31, 2017, 2016 and 2015, Westlake accounted for approximately 83.0%, 86.5% and 82.9%, respectively, of the Partnership's net sales.

General

OpCo, together with other subsidiaries of Westlake not included in these consolidated financial statements, were guarantors under Westlake's revolving credit facility and the indentures governing its senior notes. During August 2016, OpCo and certain subsidiaries of Westlake were released from their guarantees.

During August 2015, the Partnership entered into an interest rate contract with Westlake to fix the LIBOR component of the interest rate for a portion of the MLP Revolver balance.

During the years ended December 31, 2017, 2016 and 2015, the Partnership reimbursed $415, $245 and $1,033, respectively, to Westlake for certain state tax payments.

OpCo has entered into two site lease agreements with Westlake in connection with the IPO, and each has a term of 50 years. Pursuant to the site lease agreements, OpCo pays Westlake one dollar per site per year.

Unit-Based Compensation

12 Months Ended

Dec. 31, 2017

Share-based Compensation [Abstract]

Unit-Based Compensation

Unit-based Compensation

The Westlake Chemical Partners LP Long-Term Incentive Plan (the "Plan") was adopted on July 15, 2014 and provides for grants of unit options, restricted units, phantom units, unit awards, distribution equivalent rights ("DERs") and other unit-based awards. The purpose of the Plan is to attract and retain the services of individuals who are essential for the growth and profitability of the Partnership and to encourage such individuals to devote their best efforts to advancing the business of the Partnership and its affiliates. Awards under the Plan are determined by the board of directors of the Partnership's general partner or a committee thereof (the "Committee"). Under the Plan, DERs may be granted, which represent a contingent right to receive an amount in cash, units, restricted units and/or phantom units, as determined by the Committee at its sole discretion, equal in value to the cash distributions made by the Partnership with respect to a common unit during the period such award is outstanding. The terms and conditions of each award are determined by the Committee. The maximum number of common units of the Partnership that may be delivered with respect to awards under the Plan is 1,270,000. The phantom units along with a corresponding number of DERs were granted to certain non-employee directors of the general partner of the Partnership during the years ended December 31, 2017, 2016 and 2015. These phantom units vest on the third anniversary of the grant date. There were no forfeitures under the Plan during 2017, 2016 and 2015. During 2016, the vesting of 5,543 phantom units was accelerated in connection with the retirement of one of our non-employee directors. The total fair value of phantom units that vested during the year ended December 31, 2017 was $54,940.

Non-vested phantom unit awards as of December 31, 2017 and 2016 and awards granted during the respective periods were as follows:



	Number of Units		Weighted Average Fair Value
Non-vested balance at December 31, 2015	16,963		$	22.89
Granted	9,900		22.91
Vested	(5,543	)	23.38
Non-vested balance at December 31, 2016	21,320		22.77
Granted	10,146		23.75
Vested	(2,202	)	23.42
Non-vested balance at December 31, 2017	29,264		23.09

Each phantom unit represents the right to receive, upon vesting, either a cash payment equal to the fair market value of one Partnership common unit or a Partnership common unit. Each DER has distribution rights only so long as the phantom units to which it relates to has not vested or been settled.

The awards, which are classified as liability awards for financial accounting purposes, are re-measured at each reporting date until they vest. The total units available for grant at December 31, 2017 were 1,240,736. The total compensation cost recognized during the years ended December 31, 2017, 2016 and 2015 was $289, $194 and $75, respectively, and is included in selling, general and administrative expenses and classified as a liability in the consolidated financial statements of the Partnership. The unrecognized compensation cost associated with all grants under the Plan at December 31, 2017 was $330,682 and the weighted average remaining term of the units at December 31, 2017 was 1.85 years.

Fair Value Measurements

12 Months Ended

Dec. 31, 2017

Fair Value Disclosures [Abstract]

Fair Value Measurements

The Partnership reports certain assets and liabilities at fair value, which is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date (exit price). Under the accounting guidance for fair value measurements, inputs used to measure fair value are classified in one of three levels:

Level 1: Quoted market prices in active markets for identical assets or liabilities.

Level 2: Observable market-based inputs or unobservable inputs that are corroborated by market data.

Level 3: Unobservable inputs that are not corroborated by market data.

The Partnership has financial assets and liabilities subject to fair value measures. These financial assets and liabilities include cash and cash equivalents, accounts receivable, net, accounts payable and long-term debt payable to Westlake, all of which are recorded at carrying value. The amounts reported in the consolidated balance sheets for accounts receivable, net and accounts payable approximate their fair value due to the short maturities of these instruments. The carrying and fair values of the Partnership's long-term debt at December 31, 2017 and December 31, 2016 are summarized in the table below. The fair value of debt is determined based on the present value of expected future cash flows using a discounted cash flow methodology. Because the Partnership's valuation methodology used for long-term debt requires the use of significant unobservable inputs, the inputs used to measure the fair value of the Partnership's long-term debt are classified as Level 3 within the fair value hierarchy. Inputs used to estimate the fair values of the Partnership's long-term debt include the selection of an appropriate discount rate.



	December 31, 2017				December 31, 2016
	Carrying Value		Fair Value		Carrying Value		Fair Value
August 2013 Promissory Notes	$	—	$	—	$	31,775	$	31,775
OpCo Revolver	220,416		228,180		427,513		442,716
MLP Revolver	253,544		258,234		135,341		134,835

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Income Taxes

12 Months Ended

Dec. 31, 2017

Income Tax Disclosure [Abstract]

Income Taxes

The components of income tax of the Partnership are as follows:




	Year Ended December 31,
	2017		2016		2015
Current
Federal	$	—	$	—	$	—
State and local	796		691		1,128
	796		691		1,128
Deferred
Federal	—		—		—
State and local	484		344		(456		)
	484		344		(456		)
Total provision	$	1,280	$	1,035	$	672

The reconciliation of income tax expense at the U.S. statutory rate to the income tax expense is as follows:




	Year Ended December 31,
	2017			2016			2015
Provision for federal income tax, at statutory rate	$	124,018		$	124,054		$	124,083
State income tax provision, net of federal income tax effect	1,280			1,035			672
Partnership income not subject to entity-level federal income tax	(124,018		)	(124,054		)	(124,083		)
Manufacturing deduction	—			—			—
Other, net	—			—			—
Total provision	$	1,280		$	1,035		$	672

The tax effects of the principal temporary differences between financial reporting and income tax reporting are as follows:



	December 31,
	2017			2016
Property, plant and equipment	$	(2,004	)	$	(1,488	)
Turnaround costs	(216		)	(248		)
Total deferred tax liabilities	$	(2,220	)	$	(1,736	)

Balance sheet classifications
Noncurrent deferred tax liability	$	(2,220	)	$	(1,736	)
Total deferred tax liabilities	$	(2,220	)	$	(1,736	)

Supplemental Information	12 Months Ended
Supplemental Information	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Supplemental Information	Supplemental Information Accrued Liabilities Accrued liabilities were $15,697 and $15,717 at December 31, 2017 and 2016, respectively. Accruals related to accrued interest, capital expenditures, and maintenance expenses, which are components of accrued liabilities, were $4,590, $3,197 and $3,698 at December 31, 2017, respectively, and were $5,517, $2,647 and $2,586 at December 31, 2016, respectively. No other component of accrued liabilities was more than five percent of total current liabilities. Cash Flow Information Non-cash Investing Activity The change in capital expenditure accrual increasing additions to property, plant and equipment was $867 and $18,113 for the years ended December 31, 2017 and 2016, respectively. The change in capital expenditure accrual reducing additions to property, plant and equipment was $14,552 for the year ended December 31, 2015. Interest and Income Taxes Interest paid by the Partnership, net of interest capitalized, was $23,063, $9,901 and $9,538 for the years ended December 31, 2017, 2016 and 2015, respectively. Income tax paid by the Partnership was $716, $633 and $1,264 for the years ended December 31, 2017, 2016 and 2015, respectively, of which $301, $388 and $231 was paid directly to the tax authorities for the years ended December 31, 2017, 2016 and 2015, and $415, $245 and $1,033 was paid to Westlake as reimbursements for the years ended December 31, 2017, 2016 and 2015.

Commitments and Contingencies

12 Months Ended

Dec. 31, 2017

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies

The Partnership is subject to environmental laws and regulations that can impose civil and criminal sanctions and that may require the Partnership to mitigate the effects of contamination caused by the release or disposal of hazardous substances into the environment. These laws include the federal Clean Air Act, the federal Water Pollution Control Act, the Resource Conservation and Recovery Act ("RCRA"), the Comprehensive Environmental Response, Compensation, and Liability Act ("CERCLA"), the Toxic Substances Control Act and various other federal, state and local laws and regulations. Under CERCLA, an owner or operator of property may be held strictly liable for remediating contamination without regard to whether that person caused the contamination, and without regard to whether the practices that resulted in the contamination were legal at the time they occurred. Because the Partnership's production sites have a history of industrial use, it is impossible to predict precisely what effect these legal requirements will have on the Partnership. Westlake will indemnify the Partnership for liabilities that occurred or existed prior to August 4, 2014.

The Partnership is involved in various legal proceedings incidental to the conduct of its business. The Partnership does not believe that any of these legal proceedings will have a material adverse effect on its financial condition, results of operations or cash flows.

Other Commitments

The Partnership is obligated under various long-term and short-term noncancelable operating leases, primarily related to rail car leases and land. Several of the leases provide for renewal terms. At December 31, 2017, future minimum lease commitments were as follows:



2018	$	790
2019	722
2020	654
2021	539
2022	256
Thereafter	—
	$	2,961

Rental expense was approximately $2,410, $2,542 and $3,125 for the years ended December 31, 2017, 2016 and 2015, respectively.

The Partnership has various purchase commitments for its capital projects and for materials, supplies and services incident to the ordinary conduct of business.

Quarterly Financial Information (Unaudited)

12 Months Ended

Dec. 31, 2017

Quarterly Financial Information Disclosure [Abstract]

Quarterly Financial Information (Unaudited)



	Three Months Ended
	March 31, 2017		June 30, 2017		September 30, 2017		December 31, 2017
Net sales	$	277,448	$	290,113	$	296,775	$	308,645
Gross profit	97,961		99,571		95,403		110,732
Income from operations	90,133		92,685		88,598		102,991
Net income	86,028		86,470		82,245		98,315
Net income attributable to Westlake Chemical Partners LP	9,764		9,975		13,385		15,546
Net income attributable to Westlake Chemical Partners LP
Basic and diluted earnings per common unitholder	$	0.35	$	0.36	$	0.47	$	0.46
Basic and diluted earnings per subordinated unitholder	$	0.35	$	0.36	$	—	$	—
Common units outstanding	14,373,615		14,373,615		32,234,730		32,234,730
Subordinated units outstanding	12,686,115		12,686,115		—		—
	Three Months Ended
	March 31, 2016		June 30, 2016		September 30, 2016		December 31, 2016

Net sales	$	252,604	$	210,841	$	229,354	$	293,937
Gross profit	110,414		88,381		86,801		105,735
Income from operations	104,317		82,533		81,013		98,581
Net income	102,771		81,192		75,859		93,581
Net income attributable to Westlake Chemical Partners LP	12,084		9,344		8,661		10,851
Net income attributable to Westlake Chemical Partners LP
Basic and diluted earnings per common unitholder	$	0.45	$	0.34	$	0.32	$	0.39
Basic and diluted earnings per subordinated unitholder	$	0.45	$	0.34	$	0.32	$	0.39
Common units outstanding	14,373,615		14,373,615		14,373,615		14,373,615
Subordinated units outstanding	12,686,115		12,686,115		12,686,115		12,686,115

Description Of Business And Significant Accounting Policies (Policy)

12 Months Ended

Dec. 31, 2017

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Description Of Business

Description of Business

Basis of Presentation

The accompanying consolidated financial statements have been prepared in conformity with the accounting principles generally accepted in the United States.

Cash And Cash Equivalents

Cash and Cash Equivalents

Cash equivalents consist of highly liquid investments that are readily convertible into cash and have a maturity of three months or less at the date of acquisition.

Allowance For Doubtful Accounts

Allowance for Doubtful Accounts

Inventories

Property, Plant and Equipment

Depreciation is provided by utilizing the straight-line method over the estimated useful lives of the assets as follows:



Classification		Years

Buildings and improvements		40
Plant and equipment		25
Ethylene pipeline		35
Other		3-15

Impairment Of Long-Lived Assets and Intangible Assets

Impairment of Long-Lived Assets

Impairment of Goodwill and Intangible Assets

Turnaround Costs

Concentration Of Credit Risk

Concentration of Credit Risk

Revenue Recognition

Derivative Instruments

Environmental Costs

Income Taxes

Segment Reporting

The Partnership only operates one segment (ethylene production) and all of its operations are located in the United States.

Use Of Estimates

Use of Estimates

Comprehensive Income

Other Comprehensive Income

Recent Accounting Pronouncements and Recently Adopted Accounting Standards

Recent Accounting Pronouncements

Revenue from Contracts with Customers (ASU No. 2014-09)

Leases (ASU No. 2016-02)

Credit Losses (ASU No. 2016-13)

Cash Flows (ASU No. 2016-15)

Business Combinations (ASU No. 2017-01)

Other Income - Gains and Losses from the Derecognition of Nonfinancial Assets (ASU No. 2017-05)

Recently Adopted Accounting Standards

Amendments to the Consolidation Analysis (ASU No. 2016-17)

Description Of Business And Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2017

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Property, Plant and Equipment

Depreciation is provided by utilizing the straight-line method over the estimated useful lives of the assets as follows:



Classification		Years

Buildings and improvements		40
Plant and equipment		25
Ethylene pipeline		35
Other		3-15

Schedule Of Estimated Useful Lives Of Assets

Depreciation is provided by utilizing the straight-line method over the estimated useful lives of the assets as follows:



Classification		Years

Buildings and improvements		40
Plant and equipment		25
Ethylene pipeline		35
Other		3-15

Accounts Receivable—Third Parties (Tables)

12 Months Ended

Dec. 31, 2017

Accounts Receivable, Net [Abstract]

Schedule Of Accounts Receivable

Accounts receivable—third parties consist of the following:



	December 31,
	2017			2016
Trade customers	$	18,794		$	11,913
Allowance for doubtful accounts	(711		)	(564		)
	18,083			11,349
Other	—			736
Accounts receivable, net—third parties	$	18,083		$	12,085

Inventories (Tables)

12 Months Ended

Dec. 31, 2017

Inventory, Net [Abstract]

Schedule Of Inventory

Inventories consist of the following:



	December 31,
	2017		2016
Finished products	$	5,244	$	3,610
Feedstock, additives and chemicals	346		324
Inventories	$	5,590	$	3,934

Property, Plant And Equipment (Tables)

12 Months Ended

Dec. 31, 2017

Property, Plant and Equipment, Net [Abstract]

Schedule Of Property, Plant And Equipment

Property, plant and equipment consist of the following:



	December 31,
	2017			2016
Building and improvements	$	17,174		$	16,757
Plant and equipment	1,773,070			1,690,317
Other	83,167			72,215
	1,873,411			1,779,289
Less: Accumulated depreciation	(716,299		)	(644,070		)
	1,157,112			1,135,219
Construction in progress	39,133			87,019
Property, plant and equipment, net	$	1,196,245		$	1,222,238

Goodwill, Deferred Charges and Other Assets (Tables)

12 Months Ended

Dec. 31, 2017

Other Assets [Abstract]

Schedule Of Other Assets

Deferred charges and other assets, net consist of the following:



	Year Ended December 31,
	2017		2016
Interest rate contract	$	302	$	290
Turnaround costs, net	76,593		89,185
Other	4,933		5,536
Total deferred charges and other assets	$	81,828	$	95,011

Long-Term Debt (Tables)

12 Months Ended

Dec. 31, 2017

Debt Disclosure [Abstract]

Schedule Of Long-Term Debt

Long-term debt consists of the following:



	December 31,
	2017		2016
August 2013 Promissory Notes (variable interest rate of prime plus 1.5%, original scheduled maturity of August 1, 2023)	$	—	$	31,775
OpCo Revolver (variable interest rate of London Interbank Offered Rate ("LIBOR") plus 3.0%, original scheduled maturity of August 4, 2019)	220,416		427,513
MLP Revolver (variable interest rate of LIBOR plus 2.0%, original scheduled maturity of April 29, 2021)	253,544		135,341
Long-term debt payable to Westlake	$	473,960	$	594,629

- Definition

Tabular disclosure of long-debt instruments or arrangements, including identification, terms, features, collateral requirements and other information necessary to a fair presentation. These are debt arrangements that originally required repayment more than twelve months after issuance or greater than the normal operating cycle of the entity, if longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21475-112644

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=75038535&loc=d3e64711-112823

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(e),(f))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=64930739&loc=d3e28878-108400

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21538-112644

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21506-112644

Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 1A
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28541-108399

Reference 9: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28551-108399

Reference 10: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21521-112644

+ Details

Distributions and Net Income Per Limited Partner Unit (Tables)

12 Months Ended

Dec. 31, 2017

Earnings Per Share [Abstract]

Schedule of Incentive Distributions Made to Managing Members or General Partners by Distribution

If cash distributions to the Partnership's unitholders exceed $0.3163 per unit in any quarter, the Partnership's unitholders and Westlake, as the holder of the Partnership's incentive distribution rights, will receive distributions according to the following percentage allocations:



	Marginal Percentage Interest in Distributions
Total Quarterly Distribution Per Unit	Unitholders		IDR Holders
Above $0.3163 up to $0.3438	85.0	%	15.0	%
Above $0.3438 up to $0.4125	75.0	%	25.0	%
Above $0.4125	50.0	%	50.0	%

Schedule of Earnings Per Share, Basic and Diluted



	Year Ended December 31
	2017		2016		2015
Net income attributable to the Partnership	$	48,670	$	40,940	$	39,831
Less:
Limited partners' distribution declared on common units	34,909		19,016		16,980
Limited partners' distribution declared on subordinated units	9,133		16,784		14,986
Distributions declared with respect to the incentive distribution rights	1,666		281		—
Net income in excess of distribution	$	2,962	$	4,859	$	7,865



	December 31, 2017
	Limited Partners' Common Units		Limited Partners' Subordinated Units			Incentive Distribution Rights		Total
Net income attributable to the Partnership:
Distribution	$	34,909	$	9,133		$	1,666	$	45,708
Net income in excess of distribution (distribution in excess of net income)	3,101		(139		)	—		2,962
Net income	$	38,010	$	8,994		$	1,666	$	48,670
Weighted average units outstanding:
Basic and diluted	22,101,547		6,290,923					28,392,470
Net income per limited partner unit:
Basic and diluted	$	1.72	$	1.43



	December 31, 2016
	Limited Partners' Common Units		Limited Partners' Subordinated Units		Incentive Distribution Rights		Total
Net income attributable to the Partnership:
Distribution	$	19,016	$	16,784	$	281	$	36,081
Net income in excess of distribution	2,581		2,278		—		4,859
Net income	$	21,597	$	19,062	$	281	$	40,940
Weighted average units outstanding:
Basic and diluted	14,373,615		12,686,115				27,059,730
Net income per limited partner unit:
Basic and diluted	$	1.50	$	1.50



	December 31, 2015
	Limited Partners' Common Units		Limited Partners' Subordinated Units		Incentive Distribution Rights		Total
Net income attributable to the Partnership:
Distribution	$	16,980	$	14,986	$	—	$	31,966
Net income in excess of distribution	4,178		3,687		—		7,865
Net income	$	21,158	$	18,673	$	—	$	39,831
Weighted average units outstanding:
Basic and diluted	14,373,615		12,686,115				27,059,730
Net income per limited partner unit:
Basic and diluted	$	1.47	$	1.47

Related Party Transactions (Tables)

12 Months Ended

Dec. 31, 2017

Schedule of Related Party Transactions

Charges from related parties in cost of sales were as follows:



	Year Ended December 31,
	2017		2016		2015
Feedstock purchased from Westlake and included in cost of sales	$	425,255	$	287,778	$	307,582
Other charges from Westlake and included in cost of sales	96,813		85,872		74,050
Total	$	522,068	$	373,650	$	381,632

Charges from related parties included within selling, general and administrative expenses were as follows:



	Year Ended December 31,
	2017		2016		2015
Services received from Westlake and included in selling, general and administrative expenses	$	27,262	$	21,971	$	20,681

Charges from related parties for goods and services capitalized as assets were as follows:



	Year Ended December 31,
	2017		2016		2015
Goods and services purchased from Westlake and capitalized as assets	$	3,491	$	17,874	$	4,332



	December 31,
	2017		2016
Accounts payable—Westlake	$	14,027	$	12,130

Sales to related parties were as follows:



	Year Ended December 31,
	2017		2016		2015
Net sales—Westlake	$	973,081	$	853,719	$	834,918

Debt payable to related parties was as follows:



	December 31,
	2017		2016
Long-term debt payable to Westlake	$	473,960	$	594,629

Unit-Based Compensation Nonvested phantom units (Tables)

12 Months Ended

Dec. 31, 2017

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Schedule of Nonvested Restricted Stock Units Activity

Non-vested phantom unit awards as of December 31, 2017 and 2016 and awards granted during the respective periods were as follows:



	Number of Units		Weighted Average Fair Value
Non-vested balance at December 31, 2015	16,963		$	22.89
Granted	9,900		22.91
Vested	(5,543	)	23.38
Non-vested balance at December 31, 2016	21,320		22.77
Granted	10,146		23.75
Vested	(2,202	)	23.42
Non-vested balance at December 31, 2017	29,264		23.09

Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2017

Fair Value Disclosures [Abstract]

Schedule Of Carrying And Fair Values Of Long-Term Debt

The carrying and fair values of the Partnership's long-term debt at December 31, 2017 and December 31, 2016 are summarized in the table below. The fair value of debt is determined based on the present value of expected future cash flows using a discounted cash flow methodology. Because the Partnership's valuation methodology used for long-term debt requires the use of significant unobservable inputs, the inputs used to measure the fair value of the Partnership's long-term debt are classified as Level 3 within the fair value hierarchy. Inputs used to estimate the fair values of the Partnership's long-term debt include the selection of an appropriate discount rate.



	December 31, 2017				December 31, 2016
	Carrying Value		Fair Value		Carrying Value		Fair Value
August 2013 Promissory Notes	$	—	$	—	$	31,775	$	31,775
OpCo Revolver	220,416		228,180		427,513		442,716
MLP Revolver	253,544		258,234		135,341		134,835

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2017

Income Tax Disclosure [Abstract]

Schedule Of The Provision For (Benefit From) Income Taxes

The components of income tax of the Partnership are as follows:




	Year Ended December 31,
	2017		2016		2015
Current
Federal	$	—	$	—	$	—
State and local	796		691		1,128
	796		691		1,128
Deferred
Federal	—		—		—
State and local	484		344		(456		)
	484		344		(456		)
Total provision	$	1,280	$	1,035	$	672

Reconciliation Of Taxes Computed At The Statutory Rate To Income Tax Expense

The reconciliation of income tax expense at the U.S. statutory rate to the income tax expense is as follows:




	Year Ended December 31,
	2017			2016			2015
Provision for federal income tax, at statutory rate	$	124,018		$	124,054		$	124,083
State income tax provision, net of federal income tax effect	1,280			1,035			672
Partnership income not subject to entity-level federal income tax	(124,018		)	(124,054		)	(124,083		)
Manufacturing deduction	—			—			—
Other, net	—			—			—
Total provision	$	1,280		$	1,035		$	672

Schedule Of Deferred Tax Assets And Liabilities

The tax effects of the principal temporary differences between financial reporting and income tax reporting are as follows:



	December 31,
	2017			2016
Property, plant and equipment	$	(2,004	)	$	(1,488	)
Turnaround costs	(216		)	(248		)
Total deferred tax liabilities	$	(2,220	)	$	(1,736	)

Balance sheet classifications
Noncurrent deferred tax liability	$	(2,220	)	$	(1,736	)
Total deferred tax liabilities	$	(2,220	)	$	(1,736	)

Commitments And Contingencies (Tables)

12 Months Ended

Dec. 31, 2017

Commitments and Contingencies Disclosure [Abstract]

Future Minimum Lease Commitments

At December 31, 2017, future minimum lease commitments were as follows:



2018	$	790
2019	722
2020	654
2021	539
2022	256
Thereafter	—
	$	2,961

Quarterly Financial Information (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2017

Quarterly Financial Information Disclosure [Abstract]

Summary Of Quarterly Financial Information



	Three Months Ended
	March 31, 2017		June 30, 2017		September 30, 2017		December 31, 2017
Net sales	$	277,448	$	290,113	$	296,775	$	308,645
Gross profit	97,961		99,571		95,403		110,732
Income from operations	90,133		92,685		88,598		102,991
Net income	86,028		86,470		82,245		98,315
Net income attributable to Westlake Chemical Partners LP	9,764		9,975		13,385		15,546
Net income attributable to Westlake Chemical Partners LP
Basic and diluted earnings per common unitholder	$	0.35	$	0.36	$	0.47	$	0.46
Basic and diluted earnings per subordinated unitholder	$	0.35	$	0.36	$	—	$	—
Common units outstanding	14,373,615		14,373,615		32,234,730		32,234,730
Subordinated units outstanding	12,686,115		12,686,115		—		—
	Three Months Ended
	March 31, 2016		June 30, 2016		September 30, 2016		December 31, 2016

Net sales	$	252,604	$	210,841	$	229,354	$	293,937
Gross profit	110,414		88,381		86,801		105,735
Income from operations	104,317		82,533		81,013		98,581
Net income	102,771		81,192		75,859		93,581
Net income attributable to Westlake Chemical Partners LP	12,084		9,344		8,661		10,851
Net income attributable to Westlake Chemical Partners LP
Basic and diluted earnings per common unitholder	$	0.45	$	0.34	$	0.32	$	0.39
Basic and diluted earnings per subordinated unitholder	$	0.45	$	0.34	$	0.32	$	0.39
Common units outstanding	14,373,615		14,373,615		14,373,615		14,373,615
Subordinated units outstanding	12,686,115		12,686,115		12,686,115		12,686,115

Description Of Business And Significant Accounting Policies (Narrative) (Details)					12 Months Ended
	Sep. 29, 2017 USD ($) shares	Apr. 29, 2015 USD ($)	Apr. 01, 2015	Aug. 04, 2014 shares	Dec. 31, 2017 USD ($) production_facility	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Threshold period past due accounts receivable reviewed					90 days
Capitalized interest					$ 435,000	$ 5,961,000	$ 5,116,000
Goodwill					$ 5,814,000	$ 5,814,000
Amortization period, minimum (in years)					3 years
Amortization period, maximum (in years)					6 years
Finite Lived Intangible Assets Amortization Period Minimum					5 years
Other assets amortization period, maximum (in years)					15 years
Affiliated Entity [Member] \| Westlake Chemical OpCo LP [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Partnership's ownership interest (percent)	18.30%		13.30%	10.60%
Additional ownership interest acquired	5.00%	2.70%	2.70%
Amount paid to purchase additional limited partner interest	$ 229,207,000	$ 135,341,000
Limited Liability Company [Member] \| Westlake Chemical OpCo GP LLC [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Partnership's ownership interest (percent)				100.00%
Westlake [Member] \| Majority-Owned Subsidiary, Unconsolidated [Member] \| Westlake Chemical OpCo LP [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Partnership's ownership interest (percent)	81.70%
Westlake Chemical OpCo LP [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Number of Production Facilities \| production_facility					3
Limited Partner [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Number of units sold in public offering \| shares	5,175,000			12,937,500
Predecessor [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest								$ 0

Description Of Business And Significant Accounting Policies (Schedule Of Estimated Useful Lives Of Assets) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Capitalized interest	$ 435	$ 5,961	$ 5,116
Buildings And Improvements [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life (in years)	40 years
Plant And Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life (in years)	25 years
Ethylene Pipeline [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life (in years)	35 years
Minimum [Member] \| Other [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life (in years)	3 years
Maximum [Member] \| Other [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life (in years)	15 years

Initial Public Offering and Purchase of Additional Interests (Details)					12 Months Ended
	Sep. 29, 2017 USD ($) $ / shares shares	Apr. 29, 2015 USD ($)	Apr. 01, 2015	Aug. 04, 2014 lb $ / lb shares	Dec. 31, 2017 USD ($) lb $ / lb shares	Dec. 31, 2016 USD ($) shares	Dec. 31, 2015 USD ($)	Aug. 30, 2017 shares
Limited Partners' Capital Account [Line Items]
Proceeds from secondary public offering, net of finance and other offering costs	$ 110,739,000				$ 110,698,000	$ 0	$ 0
Underwriting Discounts, Structuring Fees and Offering Expenses on Issuance of Equity	$ 3,111,000
Long-term Commitment (Excluding Unconditional Purchase Obligation) [Abstract]
Increase (Decrease) in Receivables under Investment Management Agreements					$ 136,172,000	$ 0	$ 0
Westlake [Member]
Limited Partners' Capital Account [Line Items]
Number of units sold in public offering \| shares	5,175,000			12,937,500
Partners' Capital Account, Units, Sold in Public Offering, Price per Unit \| $ / shares	$ 22.00
Westlake Chemical OpCo LP [Member] \| Affiliated Entity [Member]
Limited Partners' Capital Account [Line Items]
Partnership's ownership interest (percent)	18.30%		13.30%	10.60%
Additional ownership interest acquired	5.00%	2.70%	2.70%
Amount paid to purchase additional limited partner interest	$ 229,207,000	$ 135,341,000
Westlake Chemical OpCo LP [Member] \| Ethylene Sales Agreement [Member]
Long-term Commitment (Excluding Unconditional Purchase Obligation) [Abstract]
Exchange agreement amount of purchase agreement \| lb					200,000,000
Purchase commitment, fixed margin on variable pricing \| $ / lb					0.006
Westlake Chemical OpCo LP [Member] \| Ethylene Sales Agreement [Member] \| Investee [Member]
Long-term Commitment (Excluding Unconditional Purchase Obligation) [Abstract]
Minimum percentage required to be purchased					95.00%
Westlake Chemical OpCo LP [Member] \| Westlake [Member] \| Majority-Owned Subsidiary, Unconsolidated [Member]
Limited Partners' Capital Account [Line Items]
Partnership's ownership interest (percent)	81.70%
Westlake Chemical OpCo LP [Member] \| Westlake [Member] \| Services And Secondment Agreement [Member] \| Investee [Member]
Long-term Commitment (Excluding Unconditional Purchase Obligation) [Abstract]
Related party transactions, term of agreements				12 years
Period of default in performance that can allow a party to terminate agreement				30 days
Westlake Chemical OpCo LP [Member] \| Westlake [Member] \| Ethylene Sales Agreement [Member] \| Investee [Member]
Long-term Commitment (Excluding Unconditional Purchase Obligation) [Abstract]
Term of sales agreement				12 years
Minimum percentage required to be purchased				95.00%
Maximum mass required to be purchased \| lb				3,800,000,000
Number of years used to calculate average expenses				5 years
Purchase commitment, fixed margin on variable pricing \| $ / lb				0.10
Purchase commitment, renewal term				12 months
Westlake Chemical OpCo LP [Member] \| Westlake [Member] \| Feedstock Supply Agreement [Member] \| Investee [Member]
Long-term Commitment (Excluding Unconditional Purchase Obligation) [Abstract]
Related party transactions, term of agreements				12 months
Westlake Chemical OpCo LP [Member] \| Westlake [Member] \| Excess Production Option [Member] \| Investee [Member]
Long-term Commitment (Excluding Unconditional Purchase Obligation) [Abstract]
Percentage of excess production that can be purchased				95.00%
Purchase commitment, fixed margin on variable pricing \| $ / lb				0.10
Westlake [Member] \| MLP Revolver [Member]
Long-term Commitment (Excluding Unconditional Purchase Obligation) [Abstract]
Maximum borrowing capacity		$ 300,000,000
Westlake [Member] \| Common units [Member]
Limited Partners' Capital Account [Line Items]
Units outstanding \| shares					14,122,230	1,436,115
Westlake [Member] \| Subordinated units [Member]
Limited Partners' Capital Account [Line Items]
Units outstanding \| shares					0	12,686,115		12,686,115

Accounts Receivable—Third Parties (Schedule Of Accounts Receivable) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Accounts Receivable, Net [Abstract]
Trade customers	$ 18,794	$ 11,913
Allowance for doubtful accounts	(711)	(564)
Trade Customer Receivable Net Current	18,083	11,349
Other Receivables, Net, Current	0	736
Accounts receivable, net—third parties	$ 18,083	$ 12,085

Inventories (Schedule Of Inventory) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Inventory, Net [Abstract]
Finished products	$ 5,244	$ 3,610
Feedstock, additives, and chemicals	346	324
Inventories	$ 5,590	$ 3,934

Property, Plant And Equipment (Schedule Of Property, Plant And Equipment) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment, Net [Abstract]
Building and improvements	$ 17,174	$ 16,757
Plant and equipment	1,773,070	1,690,317
Other	83,167	72,215
Property, plant and equipment, gross	1,873,411	1,779,289
Less: Accumulated depreciation	(716,299)	(644,070)
Property, plant and equipment, net, before construction in progress	1,157,112	1,135,219
Construction in progress	39,133	87,019
Property, plant and equipment, net	1,196,245	1,222,238
Depreciation expense	$ 91,154	$ 77,444	$ 64,369

Goodwill, Deferred Charges and Other Assets (Schedule Of Intangible and Other Assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Other Assets [Abstract]
Interest rate contract	$ 302	$ 290
Turnaround costs, net	76,593	89,185
Other	4,933	5,536
Total deferred charges and other assets	$ 81,828	$ 95,011

Goodwill, Deferred Charges and Other Assets (Narrative) (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Oct. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Finite-Lived Intangible Assets [Line Items]
Goodwill, Gross			$ 5,814
Discounted cash flow projections period	9 years
Rate used to discount future cash flows for goodwill impairment test	8.30%
Finite Lived Intangible Assets Amortization Period Minimum		5 years
Other assets amortization period, maximum (in years)		15 years
Other Assets [Member]
Finite-Lived Intangible Assets [Line Items]
Amortization		$ 22,831	$ 20,766	$ 16,841

Long-Term Debt (Schedule of Long-term Debt) (Details) - USD ($) $ in Thousands				12 Months Ended
	Sep. 29, 2017	Apr. 29, 2015	Apr. 01, 2015	Dec. 31, 2017	Dec. 31, 2016	Aug. 04, 2014
Related Party Transaction [Line Items]
Long-term debt				$ 473,960	$ 594,629
Weighted average interest rate on all long-term debt				3.76%	3.72%
Predecessor [Member]
Related Party Transaction [Line Items]
Long-term debt					$ 594,629
Limited Partner [Member] \| Senior Notes [Member] \| 2013 Promissory Note [Member]
Related Party Transaction [Line Items]
Long-term debt				$ 0	$ 31,775
Limited Partner [Member] \| Senior Notes [Member] \| 2013 Promissory Note [Member] \| Prime Rate [Member]
Related Party Transaction [Line Items]
Basis spread on variable rate, percent				1.50%	1.50%
Limited Partner [Member] \| Senior Notes [Member] \| 2013 Promissory Note [Member] \| Predecessor [Member]
Related Party Transaction [Line Items]
Long-term debt					$ 31,775
Limited Partner [Member] \| Senior Unsecured Revolving Credit Facility [Member] \| OpCo Revolver [Member]
Related Party Transaction [Line Items]
Long-term debt				$ 220,416	$ 427,513
Limited Partner [Member] \| Senior Unsecured Revolving Credit Facility [Member] \| OpCo Revolver [Member] \| LIBOR [Member]
Related Party Transaction [Line Items]
Basis spread on variable rate, percent				3.00%	3.00%
Limited Partner [Member] \| Senior Unsecured Revolving Credit Facility [Member] \| OpCo Revolver [Member] \| Predecessor [Member]
Related Party Transaction [Line Items]
Long-term debt					$ 427,513
Limited Partner [Member] \| Senior Unsecured Revolving Credit Facility [Member] \| MLP Revolver [Member]
Related Party Transaction [Line Items]
Long-term debt				$ 253,544	$ 135,341
Minimum [Member] \| Limited Partner [Member] \| Line of Credit [Member] \| MLP Revolver [Member] \| LIBOR [Member]
Related Party Transaction [Line Items]
Basis spread on variable rate, percent				2.00%	2.00%
Westlake [Member] \| MLP Revolver [Member]
Related Party Transaction [Line Items]
Maximum borrowing capacity		$ 300,000
Westlake [Member] \| Limited Partner [Member] \| OpCo Revolver [Member] \| Westlake Chemical OpCo LP [Member]
Related Party Transaction [Line Items]
Maximum borrowing capacity						$ 600,000
Westlake [Member] \| Limited Partner [Member] \| Line of Credit [Member] \| OpCo Revolver [Member] \| Westlake Chemical OpCo LP [Member] \| LIBOR [Member]
Related Party Transaction [Line Items]
Basis spread on variable rate, percent				3.00%
Westlake [Member] \| Limited Partner [Member] \| Line of Credit [Member] \| MLP Revolver [Member]
Related Party Transaction [Line Items]
Maximum consolidated leverage ratio during one year following acquisitions		5.50
Leverage capital ratio required during other periods		4.50
Westlake [Member] \| Minimum [Member] \| Limited Partner [Member] \| Line of Credit [Member] \| MLP Revolver [Member] \| LIBOR [Member]
Related Party Transaction [Line Items]
Basis spread on variable rate, percent		2.00%
Westlake [Member] \| Maximum [Member] \| Limited Partner [Member] \| Line of Credit [Member] \| MLP Revolver [Member] \| LIBOR [Member]
Related Party Transaction [Line Items]
Basis spread on variable rate, percent		3.00%
Westlake Chemical OpCo LP [Member] \| Affiliated Entity [Member]
Related Party Transaction [Line Items]
Additional ownership interest	5.00%	2.70%	2.70%
Amount paid to purchase additional limited partner interest	$ 229,207	$ 135,341

Distributions and Net Income Per Limited Partner Unit (Narrative) (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended
	Feb. 23, 2018	Dec. 31, 2017
Westlake Chemical OpCo LP [Member] \| Subsequent Event [Member]
Subsequent Event [Line Items]
Distribution declared per unit (usd per share)	$ 0.3864
Cash Distribution [Member] \| IDR Holders [Member] \| Subsequent Event [Member]
Subsequent Event [Line Items]
Incentive distribution	$ 614
Common units [Member] \| Cash Distribution [Member]
Subsequent Event [Line Items]
Minimum Quarterly Distribution Per Unit		$ 0.2750
Common and Subordinated units [Member] \| Cash Distribution [Member]
Subsequent Event [Line Items]
Minimum quarterly distribution per unit (usd per share)		$ 0.3163

Distributions and Net Income Per Limited Partner Unit (Incentive Distribution Rights) (Details)	12 Months Ended
	Dec. 31, 2017 $ / shares
Above $0.3163 up to $0.3438 [Member] \| Unit Holders [Member]
Distribution Made to Limited Partner [Line Items]
Marginal Percentage Interest in Distributions	85.00%
Above $0.3163 up to $0.3438 [Member] \| IDR Holders [Member]
Distribution Made to Limited Partner [Line Items]
Marginal Percentage Interest in Distributions	15.00%
Above $0.3438 up to $0.4125 [Member] \| Unit Holders [Member]
Distribution Made to Limited Partner [Line Items]
Marginal Percentage Interest in Distributions	75.00%
Above $0.3438 up to $0.4125 [Member] \| IDR Holders [Member]
Distribution Made to Limited Partner [Line Items]
Marginal Percentage Interest in Distributions	25.00%
Above $0.4125 [Member] \| Unit Holders [Member]
Distribution Made to Limited Partner [Line Items]
Marginal Percentage Interest in Distributions	50.00%
Above $0.4125 [Member] \| IDR Holders [Member]
Distribution Made to Limited Partner [Line Items]
Marginal Percentage Interest in Distributions	50.00%
Minimum [Member] \| Above $0.3163 up to $0.3438 [Member]
Distribution Made to Limited Partner [Line Items]
Quarterly distribution per unit threshold (usd per share)	$ 0.3163
Minimum [Member] \| Above $0.3438 up to $0.4125 [Member]
Distribution Made to Limited Partner [Line Items]
Quarterly distribution per unit threshold (usd per share)	0.3438
Minimum [Member] \| Above $0.4125 [Member]
Distribution Made to Limited Partner [Line Items]
Quarterly distribution per unit threshold (usd per share)	0.4125
Maximum [Member] \| Above $0.3163 up to $0.3438 [Member]
Distribution Made to Limited Partner [Line Items]
Quarterly distribution per unit threshold (usd per share)	0.3438
Maximum [Member] \| Above $0.3438 up to $0.4125 [Member]
Distribution Made to Limited Partner [Line Items]
Quarterly distribution per unit threshold (usd per share)	$ 0.4125

Distributions and Net Income Per Limited Partner Unit (Income In Excess Of Distribution) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Distribution declared									$ 45,708	$ 36,081	$ 31,966
Net income subsequent to the IPO in excess of distribution									2,962	4,859	7,865
Limited partners' interest in net income subsequent to IPO	$ 15,546	$ 13,385	$ 9,975	$ 9,764	$ 10,851	$ 8,661	$ 9,344	$ 12,084	48,670	40,940	39,831
Common units [Member]
Distribution declared									34,909	19,016	16,980
Net income subsequent to the IPO in excess of distribution									3,101	2,581	4,178
Limited partners' interest in net income subsequent to IPO									38,010	21,597	21,158
Subordinated units [Member]
Distribution declared									9,133	16,784	14,986
Net income subsequent to the IPO in excess of distribution										2,278	3,687
Limited partners' interest in net income subsequent to IPO									8,994	19,062	18,673
IDR Holders [Member]
Distributions declared with respect to the incentive distribution rights									1,666	281	0
Net income subsequent to the IPO in excess of distribution									0	0	0
Limited partners' interest in net income subsequent to IPO									1,666	281	0
Cash Distribution [Member] \| IDR Holders [Member]
Distributions declared with respect to the incentive distribution rights									$ 1,666	$ 281	$ 0

Distributions and Net Income Per Limited Partner Unit (Basic and Diluted Income Per Limited Partner Unit) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Limited Partners' Capital Account [Line Items]
Distribution									$ 45,708	$ 36,081	$ 31,966
Net income in excess of distribution									2,962	4,859	7,865
Limited partners' interest in net income subsequent to IPO	$ 15,546	$ 13,385	$ 9,975	$ 9,764	$ 10,851	$ 8,661	$ 9,344	$ 12,084	$ 48,670	$ 40,940	$ 39,831
Weighted average units outsanding:
Basic and diluted (units)									28,392,470	27,059,730	27,059,730
IDR Holders [Member]
Limited Partners' Capital Account [Line Items]
Distributions declared with respect to the incentive distribution rights									$ 1,666	$ 281	$ 0
Net income in excess of distribution									0	0	0
Limited partners' interest in net income subsequent to IPO									1,666	281	0
IDR Holders [Member] \| Cash Distribution [Member]
Limited Partners' Capital Account [Line Items]
Distributions declared with respect to the incentive distribution rights									1,666	281	0
Limited Partners' Common Units [Member]
Limited Partners' Capital Account [Line Items]
Distribution									34,909	19,016	16,980
Net income in excess of distribution									3,101	2,581	4,178
Limited partners' interest in net income subsequent to IPO									$ 38,010	$ 21,597	$ 21,158
Weighted average units outsanding:
Basic and diluted (units)	32,234,730	32,234,730	14,373,615	14,373,615	14,373,615	14,373,615	14,373,615	14,373,615	22,101,547	14,373,615	14,373,615
Net income per limited partner unit:
Income per limited partner unit (usd per unit)	$ 0.46	$ 0.47	$ 0.36	$ 0.35	$ 0.39	$ 0.32	$ 0.34	$ 0.45	$ 1.72	$ 1.50	$ 1.47
Limited Partners' Subordinated Units [Member]
Limited Partners' Capital Account [Line Items]
Distribution									$ 9,133	$ 16,784	$ 14,986
Net income in excess of distribution										2,278	3,687
Distribution in excess of net income									(139)
Limited partners' interest in net income subsequent to IPO									$ 8,994	$ 19,062	$ 18,673
Weighted average units outsanding:
Basic and diluted (units)	0	0	12,686,115	12,686,115	12,686,115	12,686,115	12,686,115	12,686,115	6,290,923	12,686,115	12,686,115
Net income per limited partner unit:
Income per limited partner unit (usd per unit)	$ 0.00	$ 0.00	$ 0.36	$ 0.35	$ 0.39	$ 0.32	$ 0.34	$ 0.45	$ 1.43	$ 1.50	$ 1.47

Related Party Transactions (Sales to Related Parties) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Related Party Transactions [Abstract]
Net sales - Westlake	$ 973,081	$ 853,719	$ 834,918

Related Party Transactions (Cost of Sales from Related Parties) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Related Party Transaction [Line Items]
Cost of sales	$ 769,314	$ 595,405	$ 624,339
Affiliated Entity [Member] \| Westlake [Member]
Related Party Transaction [Line Items]
Feedstock purchased from Westlake and included in cost of sales	425,255	287,778
Other charges from Westlake and included in cost of sales	96,813	85,872
Cost of sales	$ 522,068	$ 373,650
Predecessor [Member] \| Affiliated Entity [Member] \| Westlake [Member]
Related Party Transaction [Line Items]
Feedstock purchased from Westlake and included in cost of sales			307,582
Other charges from Westlake and included in cost of sales			74,050
Cost of sales			$ 381,632

Related Party Transactions (Services from Related Parties Included in SG&A Expenses) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Related Party Transaction [Line Items]
Services received from Westlake and included in selling, general and administrative expenses	$ 29,260	$ 24,887	$ 23,550
Affiliated Entity [Member] \| Westlake [Member]
Related Party Transaction [Line Items]
Services received from Westlake and included in selling, general and administrative expenses	$ 27,262	$ 21,971
Affiliated Entity [Member] \| Westlake [Member] \| Predecessor [Member]
Related Party Transaction [Line Items]
Services received from Westlake and included in selling, general and administrative expenses			$ 20,681

Related Party Transactions (Goods and Services from Related Parties that have been Capitalized) (Details) - Affiliated Entity [Member] - Westlake [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Related Party Transaction [Line Items]
Goods and services purchased from Westlake and capitalized as assets	$ 3,491	$ 17,874
Predecessor [Member]
Related Party Transaction [Line Items]
Goods and services purchased from Westlake and capitalized as assets			$ 4,332

Related Party Transactions (Accounts Receivable from and Accounts Payable to Related Parties) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Related Party Transaction [Line Items]
Accounts receivable, net—Westlake	$ 43,884	$ 126,977
Accounts payable—Westlake	$ 14,027	$ 12,130
Ethylene Sales Agreement [Member] \| Investee [Member] \| Westlake Chemical OpCo LP [Member]
Related Party Transaction [Line Items]
Minimum percentage required to be purchased	95.00%

Related Party Transactions (Debt Payable to Related Parties) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Related Party Transaction [Line Items]
Interest on related party debt payable	$ 21,861	$ 12,607	$ 4,967
Interest capitalized	435	5,961	$ 5,116
Accrued interest on related party debt	4,590	5,517
Long-term debt payable to Westlake	473,960	594,629
Predecessor [Member]
Related Party Transaction [Line Items]
Long-term debt payable to Westlake		594,629
Accrued Liabilities [Member] \| Affiliated Entity [Member] \| Westlake [Member]
Related Party Transaction [Line Items]
Accrued interest on related party debt	$ 4,590	$ 5,517

Related Party Transactions (General) (Details)		12 Months Ended
Related Party Transactions (General) (Details)	Aug. 04, 2014 USD ($) lease	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Related Party Transaction [Line Items]
Income Taxes Paid		$ 716,000	$ 633,000	$ 1,264,000
Affiliated Entity [Member] \| Reimbursement to Parent for State Tax [Member] \| Westlake [Member]
Related Party Transaction [Line Items]
Income Taxes Paid		$ 415,000	$ 245,000	$ 1,033,000
Investee [Member] \| Westlake [Member] \| Site Lease Agreement [Member] \| Westlake Chemical OpCo LP [Member]
Related Party Transaction [Line Items]
Number of lease agreements \| lease	2
Term of operating lease	50 years
Operating lease, rental amount	$ 1
Sales Revenue, Net [Member] \| Customer Concentration Risk [Member] \| Westlake [Member] \| Affiliated Entity [Member]
Related Party Transaction [Line Items]
Concentration Risk, Percentage		83.00%	86.50%	82.90%

Related Party Transactions Related Party Transactions (Receivable under the Investment Management Agreement) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Related Party Transactions [Abstract]
Accrued Interest on Receivables under Investment Management Agreements with Related Parties, Current	$ 340
Receivable under the Investment Management Agreement—Westlake Chemical Corporation (Westlake)	$ 136,510	$ 0

Partners' Equity (Incentive Distribution Rights) (Details) - USD ($)			12 Months Ended
	Sep. 29, 2017	Aug. 04, 2014	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Aug. 30, 2017
Class of Stock [Line Items]
Proceeds from secondary public offering, net of finance and other offering costs	$ 110,739,000		$ 110,698,000	$ 0	$ 0
Underwriting Discounts, Structuring Fees and Offering Expenses on Issuance of Equity	$ 3,111,000
Subordinated units [Member] \| Westlake [Member]
Class of Stock [Line Items]
Units outstanding			0	12,686,115		12,686,115
Limited Partner [Member]
Class of Stock [Line Items]
Number of units sold in public offering	5,175,000	12,937,500
Partners' Capital Account, Units, Sold in Public Offering, Price per Unit	$ 22.00

Unit-Based Compensation (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) director $ / shares shares	Dec. 31, 2016 USD ($) $ / shares shares	Dec. 31, 2015 USD ($) $ / shares shares	Jul. 15, 2014 shares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition	1 year 10 months 6 days
Phantom Share Units (PSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding [Roll Forward]
Beginning balance	21,320	16,963
Granted	10,146	9,900
Vested	(2,202)	(5,543)
Ending balance	29,264	21,320	16,963
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Weighted Average Fair Value, beginning balance (usd per share) \| $ / shares	$ 22.77	$ 22.89
Weighted Average Grant Date Fair Value, Granted (usd per share) \| $ / shares	23.75	22.91
Weighted Average Grant Date Fair Value, Vested (usd per share) \| $ / shares	23.42	23.38
Weighted Average Fair Value, ending balance (usd per share) \| $ / shares	$ 23.09	$ 22.77	$ 22.89
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value \| $	$ 54,940
Westlake Chemical Partners LP Long-Term Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Number of units authorized				1,270,000
Total units available for grant	1,240,736
Unrecognized compensation cost \| $	$ 330,682
Westlake Chemical Partners LP Long-Term Incentive Plan [Member] \| Selling, General and Administrative Expenses [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Total compensation cost \| $	$ 289	$ 194	$ 75
Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Deferred Compensation Arrangement with Individual, Number of Directors That Retired in Period \| director	1

Fair Value Measurements (Schedule Of Carrying And Fair Values Of Long-Term Debt) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt	$ 473,960	$ 594,629
2013 Promissory Note [Member] \| Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	0	31,775
OpCo Revolver [Member] \| Senior Unsecured Revolving Credit Facility [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	228,180	442,716
MLP Revolver [Member] \| Senior Unsecured Revolving Credit Facility [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	258,234	134,835
Limited Partner [Member] \| 2013 Promissory Note [Member] \| Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt	0	31,775
Limited Partner [Member] \| OpCo Revolver [Member] \| Senior Unsecured Revolving Credit Facility [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt	220,416	427,513
Limited Partner [Member] \| MLP Revolver [Member] \| Senior Unsecured Revolving Credit Facility [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt	$ 253,544	$ 135,341

Income Taxes (Schedule Of The Provision For (Benefit From) Income Taxes) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Federal	$ 0	$ 0	$ 0
State and local	796	691	1,128
Total Current	796	691	1,128
Federal	0	0	0
State and local	484	344	(456)
Total deferred	484	344	(456)
Total provision	$ 1,280	$ 1,035	$ 672

Income Taxes (Reconciliation Of Taxes Computed At The Statutory Rate To Income Tax Expense) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Provision for federal income tax, at statutory rate	$ 124,018	$ 124,054	$ 124,083
State income tax provision, net of federal income tax effect	1,280	1,035	672
Partnership income not subject to entity-level tax	(124,018)	(124,054)	(124,083)
Manufacturing deduction	0	0	0
Other, net	0	0	0
Total provision	$ 1,280	$ 1,035	$ 672

Income Taxes (Schedule Of Deferred Tax Assets And Liabilities) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Federal	$ 0	$ 0	$ 0
Property, plant and equipment	(2,004)	(1,488)
Turnaround costs	(216)	(248)
Deferred tax liabilities-total	(2,220)	(1,736)
Balance sheet classifications
Noncurrent deferred tax liability	(2,220)	(1,736)
State and local	796	691	1,128
Current Income Tax Expense (Benefit)	796	691	1,128
Federal	0	0	0
State and local	484	344	(456)
Deferred Income Tax Expense (Benefit)	484	344	(456)
Total provision	$ 1,280	$ 1,035	$ 672

Supplemental Information (Accrued Liabilities and Other Income, Net) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Accrued Liabilities
Accrued liabilities	$ 15,697	$ 15,717
Accrued interest	4,590	5,517
Accrual related to capital expenditures	3,197	2,647
Accrued maintenance expense	$ 3,698	$ 2,586

Supplemental Information (Cash Flow Information) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Related Party Transaction [Line Items]
Increase (decrease) in capital expenditure accrual	$ 867	$ 18,113	$ (14,552)
Interest Paid, Net	23,063	9,901	9,538
Income Taxes Paid	716	633	1,264
State and Local Jurisdiction [Member]
Related Party Transaction [Line Items]
Income Taxes Paid	301	388	231
Reimbursement to Parent for State Tax [Member] \| Westlake [Member] \| Affiliated Entity [Member]
Related Party Transaction [Line Items]
Income Taxes Paid	$ 415	$ 245	$ 1,033

Commitments And Contingencies (Future Minimum Lease Commitments) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Commitments and Contingencies Disclosure [Abstract]
2018	$ 790
2019	722
2020	654
2021	539
2022	256
Thereafter	0
Total future minimum lease commitments	2,961
Approximate rental expense	$ 2,410	$ 2,542	$ 3,125

Quarterly Financial Information (Unaudited) (Summary Of Quarterly Financial Information) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net sales	$ 308,645	$ 296,775	$ 290,113	$ 277,448	$ 293,937	$ 229,354	$ 210,841	$ 252,604	$ 1,172,981	$ 986,736	$ 1,007,221
Gross profit	110,732	95,403	99,571	97,961	105,735	86,801	88,381	110,414	403,667	391,331	382,882
Income from operations	102,991	88,598	92,685	90,133	98,581	81,013	82,533	104,317	374,407	366,444	359,332
Net income	98,315	82,245	86,470	86,028	93,581	75,859	81,192	102,771	353,058	353,403	353,853
Net income attributable to Westlake Chemical Partners LP	$ 15,546	$ 13,385	$ 9,975	$ 9,764	$ 10,851	$ 8,661	$ 9,344	$ 12,084	$ 48,670	$ 40,940	$ 39,831
Weighted Average Number of Shares Outstanding, Basic and Diluted									28,392,470	27,059,730	27,059,730
Common units [Member]
Net income attributable to Westlake Chemical Partners LP									$ 38,010	$ 21,597	$ 21,158
Basic and diluted earnings per common unit holder (usd per unit)	$ 0.46	$ 0.47	$ 0.36	$ 0.35	$ 0.39	$ 0.32	$ 0.34	$ 0.45	$ 1.72	$ 1.50	$ 1.47
Weighted Average Number of Shares Outstanding, Basic and Diluted	32,234,730	32,234,730	14,373,615	14,373,615	14,373,615	14,373,615	14,373,615	14,373,615	22,101,547	14,373,615	14,373,615
Subordinated units [Member]
Net income attributable to Westlake Chemical Partners LP									$ 8,994	$ 19,062	$ 18,673
Basic and diluted earnings per common unit holder (usd per unit)	$ 0.00	$ 0.00	$ 0.36	$ 0.35	$ 0.39	$ 0.32	$ 0.34	$ 0.45	$ 1.43	$ 1.50	$ 1.47
Weighted Average Number of Shares Outstanding, Basic and Diluted	0	0	12,686,115	12,686,115	12,686,115	12,686,115	12,686,115	12,686,115	6,290,923	12,686,115	12,686,115