Westlake Chemical Partners (WLKP) 10-Q 6 May 20 2020 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2020	Apr. 29, 2020
Document Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2020
Document Transition Report	false
Entity File Number	001-36567
Entity Registrant Name	Westlake Chemical Partners LP
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	32-0436529
Entity Address, Address Line One	2801 Post Oak Boulevard
Entity Address, Address Line Two	Suite 600
Entity Address, City or Town	Houston
Entity Address, State or Province	TX
Entity Address, Postal Zip Code	77056
City Area Code	713
Local Phone Number	585-2900
Title of 12(b) Security	Common units representing limited partnership interests
Trading Symbol	WLKP
Security Exchange Name	NYSE
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Units, Units Outstanding		35,194,545
Amendment Flag	false
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q1
Entity Central Index Key	0001604665
Current Fiscal Year End Date	--12-31

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Current assets
Cash and cash equivalents	$ 24,081	$ 19,923
Receivable under the Investment Management Agreement—Westlake Chemical Corporation (Westlake)	161,759	162,773
Accounts receivable, net—Westlake	40,560	42,847
Accounts receivable, net—third parties	13,535	9,914
Inventories	2,000	2,484
Prepaid expenses and other current assets	204	470
Total current assets	242,139	238,411
Property, plant and equipment, net	1,092,120	1,102,995
Goodwill	5,814	5,814
Deferred charges and other assets, net	42,954	46,236
Total assets	1,383,027	1,393,456
Current liabilities
Accounts payable—Westlake	4,333	15,201
Accounts payable—third parties	8,301	6,141
Accrued and other liabilities	18,032	17,507
Total current liabilities	30,666	38,849
Long-term debt payable to Westlake	399,674	399,674
Deferred income taxes	1,649	1,649
Other liabilities	947	1,149
Total liabilities	432,936	441,321
Commitments and contingencies (Note 13)
EQUITY
Total Westlake Chemical Partners LP partners' capital	278,670	277,514
Noncontrolling interest in Westlake Chemical OpCo LP (OpCo)	671,421	674,621
Total equity	950,091	952,135
Total liabilities and equity	1,383,027	1,393,456
Limited Partner [Member] | Common units [Member] | Publicly and Privately Held [Member]
EQUITY
Limited Partners' Capital Account	472,428	471,736
Total equity	472,428	471,736
Limited Partner [Member] | Common units [Member] | Westlake [Member]
EQUITY
Limited Partners' Capital Account	48,814	48,350
Total equity	48,814	48,350
General Partner [Member] | Westlake [Member]
EQUITY
General partner—Westlake	(242,572)	(242,572)
Total equity	$ (242,572)	$ (242,572)

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - Common units [Member] - shares	Mar. 31, 2020	Dec. 31, 2019
Publicly and Privately Held [Member]
Units issued	21,072,315	21,072,315
Units outstanding	21,072,315	21,072,315
Westlake [Member]
Units issued	14,122,230	14,122,230
Units outstanding	14,122,230	14,122,230

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Weighted Average Number of Limited Partnership and General Partnership Unit Outstanding, Basic and Diluted	35,194,545	32,345,398
Net sales—Westlake	$ 214,828	$ 257,040
Total net sales	250,549	299,086
Cost of sales	147,001	208,432
Gross profit	103,548	90,654
Selling, general and administrative expenses	6,196	6,973
Income from operations	97,352	83,681
Other income (expense)
Interest expense—Westlake	(3,950)	(5,900)
Other income, net	585	815
Income before income taxes	93,987	78,596
Income tax provision	217	200
Net income	93,770	78,396
Less: Net income attributable to noncontrolling interest in OpCo	76,023	63,441
Net income attributable to Westlake Chemical Partners LP and limited partners' interest in net income	$ 17,747	$ 14,955
Common units [Member]
Weighted Average Number of Limited Partnership and General Partnership Unit Outstanding, Basic and Diluted	35,194,545	32,345,398
Other income (expense)
Net income attributable to Westlake Chemical Partners LP and limited partners' interest in net income	$ 17,747	$ 14,955
Net Income (Loss), Per Outstanding Limited Partnership Unit, Basic, Net of Tax	$ 0.50	$ 0.46
Common units [Member] | Publicly and Privately Held [Member]
Weighted Average Number of Limited Partnership and General Partnership Unit Outstanding, Basic and Diluted	21,072,315	18,223,168
Common units [Member] | Westlake [Member]
Weighted Average Number of Limited Partnership and General Partnership Unit Outstanding, Basic and Diluted	14,122,230	14,122,230
Product and Service, Other [Member]
Total net sales	$ 35,721	$ 42,046

Consolidated Statements of Chan

Consolidated Statements of Changes in Equity - USD ($) $ in Thousands	Total	Noncontrolling Interest in OpCo [Member]	Westlake [Member]General Partner [Member]	Common units [Member]Publicly and Privately Held [Member]Limited Partner [Member]	Common units [Member]Westlake [Member]Limited Partner [Member]
Equity, beginning balance at Dec. 31, 2018	$ 934,081	$ 718,271	$ (242,572)	$ 409,608	$ 48,774
Net income	78,396	63,441	0	8,422	6,533
Net proceeds from private placement of common units	62,934			62,934
Quarterly distribution to unitholders	(13,957)			(7,845)	(6,112)
Quarterly distribution to noncontrolling interest retained in OpCo by Westlake	(81,507)	(81,507)
Equity, ending balance at Mar. 31, 2019	979,947	700,205	(242,572)	473,119	49,195
Equity, beginning balance at Dec. 31, 2019	952,135	674,621	(242,572)	471,736	48,350
Net income	93,770	76,023		10,626	7,121
Net proceeds from private placement of common units	0
Quarterly distribution to unitholders	(16,591)			(9,934)	(6,657)
Quarterly distribution to noncontrolling interest retained in OpCo by Westlake	(79,223)	(79,223)
Equity, ending balance at Mar. 31, 2020	$ 950,091	$ 671,421	$ (242,572)	$ 472,428	$ 48,814

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Cash flows from operating activities
Net income	$ 93,770	$ 78,396
Adjustments to reconcile net income to net cash provided by operating activities
Depreciation and amortization	26,031	26,844
Loss from disposition of property, plant and equipment	97	458
Other losses (gains), net	119	(180)
Changes in operating assets and liabilities
Accounts receivable—third parties	(3,740)	1,102
Net accounts receivable—Westlake	(8,573)	1,479
Inventories	484	(587)
Prepaid expenses and other current assets	266	119
Accounts payable	1,463	2,497
Accrued and other liabilities	1,252	3,472
Other, net	(208)	(101)
Cash flows from investing activities	110,961	113,499
Cash flows from investing activities
Additions to property, plant and equipment	(11,989)	(12,144)
Maturities of investments with Westlake under the Investment Management Agreement	79,000	80,000
Investments with Westlake under the Investment Management Agreement	(78,000)	(207,512)
Other	0	46
Net cash used for investing activities	(10,989)	(139,610)
Cash flows from financing activities
Net proceeds from private placement of common units	0	62,934
Quarterly distributions to noncontrolling interest retained in OpCo by Westlake	(79,223)	(81,507)
Quarterly distributions to unitholders	(16,591)	(13,957)
Net cash provided by (used for) financing activities	(95,814)	90,982
Net increase in cash and cash equivalents	4,158	64,871
Cash and cash equivalents at beginning of period	19,923	19,744
Cash and cash equivalents at end of period	$ 24,081	$ 84,615

Description of Business and Bas

Description of Business and Basis of Presentation	3 Months Ended
	Mar. 31, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Description of Business and Basis of Presentation	Description of Business and Basis of Presentation Description of Business Westlake Chemical Partners LP (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 its initial public offering (the "IPO") of 12,937,500 common units representing limited partner interests. 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 one common carrier ethylene pipeline. On March 29, 2019, the Partnership purchased an additional 4.5% newly-issued limited partner interest in OpCo for approximately $201,445 , resulting in an aggregate 22.8% limited partner interest in OpCo, effective January 1, 2019. The remaining 77.2% limited partner interest in OpCo is owned by Westlake Chemical Corporation. Basis of Presentation The accompanying unaudited consolidated interim financial statements were prepared in accordance with the rules and regulations of the Securities and Exchange Commission (the "SEC") for interim periods. Accordingly, certain information and footnotes required for complete financial statements under generally accepted accounting principles in the United States ("U.S. GAAP") have not been included. These interim consolidated financial statements should be read in conjunction with the consolidated financial statements and notes thereto of the Partnership included in the annual report on Form 10-K for the fiscal year ended December 31, 2019 (the " 2019 Form 10-K"), filed with the SEC on February 28, 2020 . These financial statements have been prepared in conformity with the accounting principles and practices as disclosed in the notes to the consolidated financial statements of the Partnership for the fiscal year ended December 31, 2019 with the exceptions of those accounting standards adopted in 2020 as discussed in Note 1 . References to "Westlake" refer collectively to Westlake Chemical Corporation and its subsidiaries, other than the Partnership, OpCo and OpCo GP. The Partnership holds a 22.8% limited partner interest and the entire non-economic general partner interest in OpCo. The remaining 77.2% 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 77.2% is recorded as noncontrolling interest in the Partnership's consolidated financial statements. In the opinion of the Partnership's management, the accompanying unaudited consolidated interim financial statements reflect all adjustments (consisting only of normal recurring adjustments) that are necessary for a fair statement of the Partnership's financial position as of March 31, 2020 , its results of operations for the three months ended March 31, 2020 and 2019 and the changes in its cash position for the three months ended March 31, 2020 and 2019 . Results of operations and changes in cash position for the interim periods presented are not necessarily indicative of the results that will be realized for the fiscal year ending December 31, 2020 or any other interim period. The preparation of financial statements in conformity with U.S. GAAP 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 materially from those estimates. Recent Accounting Pronouncements Reference Rate Reform (ASU No. 2020-04) In March 2020, the FASB issued an accounting standards update to provide optional expedients and exceptions for applying generally accepted accounting principles to contracts, hedging relationships and other transactions affected by reference rate reform if certain criteria are met. The amendments in this update are effective for all entities as of March 12, 2020 through December 31, 2022. The Partnership is in the process of evaluating the impact that the new accounting guidance will have on the Partnership's consolidated financial position, results of operations and cash flows. Recently Adopted Accounting Standards 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 trade receivables and 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 became effective for reporting periods beginning after December 15, 2019 and did not have a material impact on the Partnership's consolidated financial position, results of operations and cash flows. Fair Value Measurement (ASU No. 2018-13) In August 2018, the FASB issued an accounting standards update to modify the disclosure requirements on fair value measurements. The amendments became effective for reporting periods beginning after December 15, 2019. An entity is permitted to early adopt any removed or modified disclosures and delay adoption of the additional disclosures until the effective date. Most amendments should be applied retrospectively but certain amendments should be applied prospectively. The Partnership adopted this accounting standard effective January 1, 2020 and the adoption did not have a material impact on the Partnership's consolidated financial position, results of operations and cash flows.

Accounts Receivable - Third Par

Accounts Receivable - Third Parties	3 Months Ended
	Mar. 31, 2020
Accounts Receivable, after Allowance for Credit Loss [Abstract]
Accounts Receivable - Third Parties	Accounts Receivable—Third Parties Accounts receivable—third parties consist of the following: March 31, December 31, Trade customers $ 11,013 $ 9,730 Allowance for credit losses (596 ) (476 ) 10,417 9,254 Other receivables 3,118 660 Accounts receivable, net—third parties $ 13,535 $ 9,914

Inventories

Inventories	3 Months Ended
	Mar. 31, 2020
Inventory Disclosure [Abstract]
Inventories	Inventories Inventories consist of the following: March 31, December 31, Finished products $ 1,532 $ 2,154 Feedstock, additives and chemicals 468 330 Inventories $ 2,000 $ 2,484

Property, Plant and Equipment

Property, Plant and Equipment	3 Months Ended
	Mar. 31, 2020
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment	Property, Plant and Equipment Depreciation expense on property, plant and equipment of $22,753 and $22,214 is included in cost of sales in the consolidated statements of operations for the three months ended March 31, 2020 and 2019

Deferred Charges and Other Asse

Deferred Charges and Other Assets	3 Months Ended
	Mar. 31, 2020
Other Assets, Noncurrent [Abstract]
Deferred Charges and Other Assets	Deferred Charges and Other Assets Amortization expense on other assets of $3,278 and $4,630 is included in costs of sales in the consolidated statements of operations for the three months ended March 31, 2020 and 2019

Distributions and Net Income Pe

Distributions and Net Income Per Limited Partner Unit	3 Months Ended
	Mar. 31, 2020
Earnings Per Share [Abstract]
Distributions and Net Income Per Limited Partner Unit	Distributions and Net Income Per Limited Partner Unit On April 30, 2020 , the board of directors of Westlake Chemical Partners GP LLC ("Westlake GP"), the Partnership's general partner, declared a quarterly cash distribution for the three months ended March 31, 2020 of $0.4714 per unit. This distribution is payable on May 26, 2020 to the unitholders of record as of May 11, 2020 . 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. Three Months Ended March 31, 2020 2019 Net income attributable to the Partnership $ 17,747 $ 14,955 Less: Limited partners' distribution declared on common units 16,591 15,666 Net income in excess of distribution (distribution in excess of net income) $ 1,156 $ (711 ) Net income per unit applicable to common limited partner units is computed by dividing the respective limited partners' interest in net income by the weighted-average number of common 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 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. Three Months Ended March 31, 2020 Limited Partners' Common Units Incentive Distribution Rights Total Net income attributable to the Partnership: Distribution $ 16,591 $ — $ 16,591 Net income in excess of distribution 1,156 — 1,156 Net income $ 17,747 $ — $ 17,747 Weighted average units outstanding: Basic and diluted 35,194,545 35,194,545 Net income per limited partner unit: Basic and diluted $ 0.50 Three Months Ended March 31, 2019 Limited Partners' Common Units Incentive Distribution Rights Total Net income attributable to the Partnership: Distribution $ 15,666 $ — $ 15,666 Distribution in excess of net income (711 ) — (711 ) Net income $ 14,955 $ — $ 14,955 Weighted average units outstanding: Basic and diluted 32,345,398 32,345,398 Net income per limited partner unit: Basic and diluted $ 0.46 The amended Partnership Agreement provides that the Partnership will distribute cash each quarter to all the unitholders, pro rata, until each unit has received a distribution of $1.2938 . If cash distributions to the Partnership's unitholders exceed $1.2938 per common 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 $1.2938 up to $1.4063 85.0 % 15.0 % Above $1.4063 up to $1.6875 75.0 % 25.0 % Above $1.6875 50.0 % 50.0 % The Partnership's distribution for the three months ended March 31, 2020 did not exceed the $1.2938 per unit threshold, and, as a result, no distribution was made with respect to the Partnership's incentive distribution rights to Westlake, as the holder of the Partnership's incentive distribution rights. Distribution Per Common Unit Distributions per common unit for the three months ended March 31, 2020 and 2019 were as follows: Three Months Ended March 31, 2020 2019 Distributions per common unit $ 0.4714 $ 0.4328

Partners' Equity

Partners' Equity	3 Months Ended
	Mar. 31, 2020
Equity [Abstract]
Partners' Equity	7. Partners' Equity On October 4, 2018, the Partnership and Westlake Chemical Partners GP LLC, the general partner of the Partnership, entered into an Equity Distribution Agreement with UBS Securities LLC, Barclays Capital Inc., Citigroup Global Markets Inc., Deutsche Bank Securities Inc., RBC Capital Markets, LLC, Merrill Lynch, Pierce, Fenner & Smith Incorporated and Wells Fargo Securities, LLC to offer and sell the Partnership's common units, from time to time, up to an aggregate offering amount of $50,000 . The Equity Distribution Agreement was amended on February 28, 2020 to reference a new shelf registration for utilization under this agreement. No common units were issued under this program as of March 31, 2020 . On March 29, 2019, the Partnership completed the issuance and sale of 2,940,818 common units at a price of $21.40 per unit through a private placement. Net proceeds to the Partnership from the sale of the units were approximately $62,934 . TTWF LP, Westlake's principal stockholder and a related party, acquired 1,401,869 common units out of 2,940,818 common units issued in the private placement.

Related Party Transactions

Related Party Transactions	3 Months Ended
	Mar. 31, 2020
Related Party Transactions [Abstract]
Related Party Transactions	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: Three Months Ended March 31, 2020 2019 Net sales—Westlake $ 214,828 $ 257,040 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: Three Months Ended March 31, 2020 2019 Feedstock purchased from Westlake and included in cost of sales $ 59,638 $ 122,155 Other charges from Westlake and included in cost of sales 24,100 27,572 Total $ 83,738 $ 149,727 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: Three Months Ended March 31, 2020 2019 Services received from Westlake and included in selling, general and administrative expenses $ 5,115 $ 6,603 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: Three Months Ended March 31, 2020 2019 Goods and services purchased from Westlake and capitalized as assets $ 480 $ 643 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 $587 and $601 was included in the receivable under the Investment Management Agreement balance at March 31, 2020 and December 31, 2019 , respectively. Total interest earned related to the Investment Management Agreement was $587 and $818 for the three months ended March 31, 2020 and 2019 , respectively. The Partnership's receivable under the Investment Management Agreement was as follows: March 31, December 31, Receivable under the Investment Management Agreement $ 161,759 $ 162,773 Accounts Receivables The Partnership's accounts receivable from Westlake result primarily from ethylene sales to Westlake under the Ethylene Sales Agreement. The Partnership's accounts receivable from Westlake were as follows: March 31, December 31, Accounts receivable—Westlake $ 40,560 $ 42,847 Accounts Payable to Related Parties 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 related party accounts payable balances were as follows: March 31, December 31, Accounts payable—Westlake $ 4,333 $ 15,201 Related Party Leases OpCo is obligated to Westlake under various long-term and short-term noncancelable operating leases, primarily related to rail car leases and land. Operating lease rentals paid to Westlake for such leases were $670 and $514 for the three months ended March 31, 2020 and 2019 , respectively, and reflected in other charges from Westlake that are included in cost of sales. OpCo has two site lease agreements with Westlake, each of which has a term of 50 years. Pursuant to the site lease agreements, OpCo pays Westlake one dollar per site per year. Debt Payable to Related Parties See Note 9 for a description of related party debt payable balances. Interest on related party debt payable balances for the three months ended March 31, 2020 and 2019 was $3,950 and $5,900 , respectively. Interest on related party debt payable is presented as interest expense—Westlake in the consolidated statements of operations. Interest capitalized as a component of property, plant and equipment on related party debt was $0 for the three months ended March 31, 2020 and 2019 . At March 31, 2020 and December 31, 2019 , accrued interest on related party debt was $3,950 and $4,187 , respectively, and is reflected as a component of accrued liabilities in the consolidated balance sheets. Debt payable to related parties was as follows: March 31, December 31, Long-term debt payable to Westlake $ 399,674 $ 399,674 Major Customer and Concentration of Credit Risk During the three months ended March 31, 2020 and 2019 , Westlake accounted for approximately 85.7% and 85.9% , respectively, of the Partnership's net sales. Other See Note 7 above for an additional related party transaction.

Long-term Debt Payable to Westl

Long-term Debt Payable to Westlake	3 Months Ended
	Mar. 31, 2020
Related Party Transactions [Abstract]
Long-term Debt Payable to Westlake	Long-term Debt Payable to Westlake Long-term debt payable to Westlake consists of the following: March 31, December 31, OpCo Revolver (variable interest rate of London Interbank Offered Rate ("LIBOR") plus 2.0%, scheduled maturity of September 25, 2023) $ 22,619 $ 22,619 MLP Revolver (variable interest rate of LIBOR plus 2.0%, scheduled maturity of March 19, 2023) 377,055 377,055 $ 399,674 $ 399,674 On April 30, 2019, the Partnership repaid $201,445 of borrowings under the OpCo Revolver. On March 29, 2019, the Partnership borrowed $123,512 under the MLP Revolver to partially fund the purchase of the additional 4.5% interest in OpCo. On March 19, 2020, the Partnership entered into an amendment to the MLP Revolver, to extend the maturity date to March 19, 2023 and add a phase-out provision for LIBOR, which is to be replaced by an alternate benchmark rate. The amended Credit Agreement bears interest at a variable rate of either (a) LIBOR plus 2.0% or, if LIBOR is no longer available, (b) Alternate Base Rate plus 1.0% . The weighted average interest rate on all long-term debt was 3.9% and 4.1% , respectively, at March 31, 2020 and December 31, 2019 . As of March 31, 2020 , the Partnership was in compliance with all of the covenants under the OpCo Revolver and the MLP Revolver.

Derivative Commodity Instrument

Derivative Commodity Instruments Derivative Commodity Instruments	3 Months Ended
	Mar. 31, 2020
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Commodity Instruments	Derivative Commodity Instruments From time to time, the Partnership uses derivative instruments to reduce price volatility risk on commodities, primarily ethane and ethylene. The Partnership does not use derivative instruments to engage in speculative activities. The Partnership had no derivatives that were designated as fair value hedges during the three months ended March 31, 2020 and 2019 . Gains and losses from changes in the fair value of derivative instruments that are not designated as hedging instruments were included in net sales and cost of sales in the consolidated statements of operations for the three months ended March 31, 2020 and 2019 . The exposure on commodity derivatives used for price risk management includes the risk that the counterparty will not pay if the market price declines below the established fixed price. In such case, the Partnership would lose the benefit of the derivative differential on the volume of the commodities covered. In any event, the Partnership would continue to receive the market price on the actual volume hedge. The Partnership also bears the risk that it could lose the benefit of market improvements over the fixed derivative price for the term and volume of the derivative instruments (as such improvements would accrue to the benefit of the counterparty). The Partnership had non-hedge designated derivatives covering approximately 22.7 million gallons and 54.0 million pounds of commodities as of March 31, 2020 and 39.1 million gallons and 93.0 million pounds of commodities as of December 31, 2019 . At March 31, 2020 , the fair values of these derivative instruments recorded as accrued liabilities and accounts receivable, net were $1,708 and $2,838 , respectively. At December 31, 2019 , the fair values of these derivative instruments recorded as accrued liabilities and accounts receivable, net were $1,959 and $597 , respectively. The gains recognized in net sales and losses recognized in cost of sales related to derivatives were $3,354 and $1,448 , respectively, for the three months ended March 31, 2020 and $2,211 and $880 , respectively, for the three months ended March 31, 2019 . The Partnership's commodity contracts are measured using forward curves supplied by industry recognized sources and unrelated third-party services and classified as Level 2 under the fair value measurement guidance.

Fair Value Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2020
Fair Value Disclosures [Abstract]
Fair Value Measurements	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 March 31, 2020 and December 31, 2019 are summarized in the table below. The Partnership's long-term debt includes the OpCo Revolver and the MLP Revolver at March 31, 2020 . 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. March 31, 2020 December 31, 2019 Carrying Value Fair Value Carrying Value Fair Value OpCo Revolver $ 22,619 $ 20,864 $ 22,619 $ 23,364 MLP Revolver 377,055 380,737 377,055 379,452

Supplemental Information

Supplemental Information	3 Months Ended
	Mar. 31, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Supplemental Information	Supplemental Information Accrued Liabilities Accrued liabilities were $18,032 and $17,507 at March 31, 2020 and December 31, 2019 , respectively. Accrued interest, accrued taxes, accrued maintenance, commodity derivative related accrual, and accrued capital expenditures, which are components of accrued liabilities, were $3,950 , $3,536 , $3,769 , $1,708 and $1,630 , respectively, at March 31, 2020 and $4,187 , $2,611 , $3,225 , $1,959 and $2,375 , respectively, at December 31, 2019 . No other component of accrued liabilities was more than five percent of total current liabilities. Non-cash Investing Activity The non-cash investing activities related to accruals for capital expenditures were $20 and $52 for the three months ended March 31, 2020 and 2019, respectively.

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2020
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	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.

Subsequent Events

Subsequent Events	3 Months Ended
	Mar. 31, 2019
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events On March 11, 2020, the World Health Organization declared the ongoing coronavirus (COVID-19) outbreak a pandemic and recommended containment and mitigation measures worldwide. The pandemic has resulted in widespread adverse impacts on the global economy and on our employees, customers and suppliers.

Description of Business and B_2

Description of Business and Basis of Presentation (Policies)	3 Months Ended
	Mar. 31, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited consolidated interim financial statements were prepared in accordance with the rules and regulations of the Securities and Exchange Commission (the "SEC") for interim periods. Accordingly, certain information and footnotes required for complete financial statements under generally accepted accounting principles in the United States ("U.S. GAAP") have not been included. These interim consolidated financial statements should be read in conjunction with the consolidated financial statements and notes thereto of the Partnership included in the annual report on Form 10-K for the fiscal year ended December 31, 2019 (the " 2019 Form 10-K"), filed with the SEC on February 28, 2020 . These financial statements have been prepared in conformity with the accounting principles and practices as disclosed in the notes to the consolidated financial statements of the Partnership for the fiscal year ended December 31, 2019 with the exceptions of those accounting standards adopted in 2020 as discussed in Note 1 . References to "Westlake" refer collectively to Westlake Chemical Corporation and its subsidiaries, other than the Partnership, OpCo and OpCo GP. The Partnership holds a 22.8% limited partner interest and the entire non-economic general partner interest in OpCo. The remaining 77.2% 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 77.2% is recorded as noncontrolling interest in the Partnership's consolidated financial statements. In the opinion of the Partnership's management, the accompanying unaudited consolidated interim financial statements reflect all adjustments (consisting only of normal recurring adjustments) that are necessary for a fair statement of the Partnership's financial position as of March 31, 2020 , its results of operations for the three months ended March 31, 2020 and 2019 and the changes in its cash position for the three months ended March 31, 2020 and 2019 . Results of operations and changes in cash position for the interim periods presented are not necessarily indicative of the results that will be realized for the fiscal year ending December 31, 2020 or any other interim period. The preparation of financial statements in conformity with U.S. GAAP 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 materially from those estimates.
Recent Accounting Pronouncements	Recent Accounting Pronouncements Reference Rate Reform (ASU No. 2020-04) In March 2020, the FASB issued an accounting standards update to provide optional expedients and exceptions for applying generally accepted accounting principles to contracts, hedging relationships and other transactions affected by reference rate reform if certain criteria are met. The amendments in this update are effective for all entities as of March 12, 2020 through December 31, 2022. The Partnership is in the process of evaluating the impact that the new accounting guidance will have on the Partnership's consolidated financial position, results of operations and cash flows. Recently Adopted Accounting Standards 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 trade receivables and 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 became effective for reporting periods beginning after December 15, 2019 and did not have a material impact on the Partnership's consolidated financial position, results of operations and cash flows. Fair Value Measurement (ASU No. 2018-13) In August 2018, the FASB issued an accounting standards update to modify the disclosure requirements on fair value measurements. The amendments became effective for reporting periods beginning after December 15, 2019. An entity is permitted to early adopt any removed or modified disclosures and delay adoption of the additional disclosures until the effective date. Most amendments should be applied retrospectively but certain amendments should be applied prospectively. The Partnership adopted this accounting standard effective January 1, 2020 and the adoption did not have a material impact on the Partnership's consolidated financial position, results of operations and cash flows.

Accounts Receivable - Third P_2

Accounts Receivable - Third Parties (Tables)	3 Months Ended
	Mar. 31, 2020
Accounts Receivable, after Allowance for Credit Loss [Abstract]
Schedule Of Accounts Receivable - Third Parties	Accounts receivable—third parties consist of the following: March 31, December 31, Trade customers $ 11,013 $ 9,730 Allowance for credit losses (596 ) (476 ) 10,417 9,254 Other receivables 3,118 660 Accounts receivable, net—third parties $ 13,535 $ 9,914

Inventories (Tables)

Inventories (Tables)	3 Months Ended
	Mar. 31, 2020
Inventory Disclosure [Abstract]
Schedule Of Inventory	Inventories consist of the following: March 31, December 31, Finished products $ 1,532 $ 2,154 Feedstock, additives and chemicals 468 330 Inventories $ 2,000 $ 2,484

Distributions and Net Income _2

Distributions and Net Income Per Limited Partner Unit (Tables)	3 Months Ended
	Mar. 31, 2020
Earnings Per Share [Abstract]
Distributions Made to Limited Partner, by Distribution [Table Text Block]	If cash distributions to the Partnership's unitholders exceed $1.2938 per common 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 $1.2938 up to $1.4063 85.0 % 15.0 % Above $1.4063 up to $1.6875 75.0 % 25.0 % Above $1.6875 50.0 % 50.0 % The Partnership's distribution for the three months ended March 31, 2020 did not exceed the $1.2938 per unit threshold, and, as a result, no distribution was made with respect to the Partnership's incentive distribution rights to Westlake, as the holder of the Partnership's incentive distribution rights. Distribution Per Common Unit Distributions per common unit for the three months ended March 31, 2020 and 2019 were as follows: Three Months Ended March 31, 2020 2019 Distributions per common unit $ 0.4714 $ 0.4328
Schedule of Incentive Distributions Made to Managing Members or General Partners by Distribution	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. Three Months Ended March 31, 2020 2019 Net income attributable to the Partnership $ 17,747 $ 14,955 Less: Limited partners' distribution declared on common units 16,591 15,666 Net income in excess of distribution (distribution in excess of net income) $ 1,156 $ (711 )
Schedule of Earnings Per Share, Basic and Diluted	Net income per unit applicable to common limited partner units is computed by dividing the respective limited partners' interest in net income by the weighted-average number of common 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 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. Three Months Ended March 31, 2020 Limited Partners' Common Units Incentive Distribution Rights Total Net income attributable to the Partnership: Distribution $ 16,591 $ — $ 16,591 Net income in excess of distribution 1,156 — 1,156 Net income $ 17,747 $ — $ 17,747 Weighted average units outstanding: Basic and diluted 35,194,545 35,194,545 Net income per limited partner unit: Basic and diluted $ 0.50 Three Months Ended March 31, 2019 Limited Partners' Common Units Incentive Distribution Rights Total Net income attributable to the Partnership: Distribution $ 15,666 $ — $ 15,666 Distribution in excess of net income (711 ) — (711 ) Net income $ 14,955 $ — $ 14,955 Weighted average units outstanding: Basic and diluted 32,345,398 32,345,398 Net income per limited partner unit: Basic and diluted $ 0.46

Related Party Transactions (Tab

Related Party Transactions (Tables)	3 Months Ended
	Mar. 31, 2020
Related Party Transactions [Abstract]
Schedule of Related Party Transactions	Charges from related parties for goods and services capitalized as assets were as follows: Three Months Ended March 31, 2020 2019 Goods and services purchased from Westlake and capitalized as assets $ 480 $ 643 Sales to related parties were as follows: Three Months Ended March 31, 2020 2019 Net sales—Westlake $ 214,828 $ 257,040 The Partnership's receivable under the Investment Management Agreement was as follows: March 31, December 31, Receivable under the Investment Management Agreement $ 161,759 $ 162,773 The Partnership's accounts receivable from Westlake were as follows: March 31, December 31, Accounts receivable—Westlake $ 40,560 $ 42,847 Charges from related parties included within selling, general and administrative expenses were as follows: Three Months Ended March 31, 2020 2019 Services received from Westlake and included in selling, general and administrative expenses $ 5,115 $ 6,603 Charges from related parties in cost of sales were as follows: Three Months Ended March 31, 2020 2019 Feedstock purchased from Westlake and included in cost of sales $ 59,638 $ 122,155 Other charges from Westlake and included in cost of sales 24,100 27,572 Total $ 83,738 $ 149,727 Debt payable to related parties was as follows: March 31, December 31, Long-term debt payable to Westlake $ 399,674 $ 399,674 The related party accounts payable balances were as follows: March 31, December 31, Accounts payable—Westlake $ 4,333 $ 15,201

Long-term Debt Payable to Wes_2

Long-term Debt Payable to Westlake (Tables)	3 Months Ended
	Mar. 31, 2020
Related Party Transactions [Abstract]
Related Party Transactions, Long-term Debt	Long-term debt payable to Westlake consists of the following: March 31, December 31, OpCo Revolver (variable interest rate of London Interbank Offered Rate ("LIBOR") plus 2.0%, scheduled maturity of September 25, 2023) $ 22,619 $ 22,619 MLP Revolver (variable interest rate of LIBOR plus 2.0%, scheduled maturity of March 19, 2023) 377,055 377,055 $ 399,674 $ 399,674

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2020
Fair Value Disclosures [Abstract]
Summary Of Carrying And Fair Values Of Long-Term Debt	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 March 31, 2020 and December 31, 2019 are summarized in the table below. The Partnership's long-term debt includes the OpCo Revolver and the MLP Revolver at March 31, 2020 . 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. March 31, 2020 December 31, 2019 Carrying Value Fair Value Carrying Value Fair Value OpCo Revolver $ 22,619 $ 20,864 $ 22,619 $ 23,364 MLP Revolver 377,055 380,737 377,055 379,452

Description of Business and B_3

Description of Business and Basis of Presentation (Details) - Ownership [Domain] - USD ($) $ in Thousands	Mar. 29, 2019	Aug. 04, 2014
Westlake Chemical OpCo GP LLC [Member] | Limited Liability Company [Member]
Limited Partners' Capital Account [Line Items]
Limited partner interest		100.00%
Westlake Chemical OpCo LP [Member] | Affiliated Entity [Member]
Limited Partners' Capital Account [Line Items]
Limited partner interest	22.80%	10.60%
Amount paid to purchase additional limited partner interest	$ 201,445
Westlake [Member] | Westlake Chemical OpCo LP [Member] | Majority-Owned Subsidiary, Unconsolidated [Member]
Limited Partners' Capital Account [Line Items]
Limited partner interest	77.20%

Accounts Receivable - Third P_3

Accounts Receivable - Third Parties Accounts Receivable—Third Parties (Schedule Of Accounts Receivable) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Accounts Receivable, after Allowance for Credit Loss [Abstract]
Trade customers	$ 11,013	$ 9,730
Allowance for credit losses	(596)	(476)
Trade Customer Receivable Net Current	10,417	9,254
Other receivables	3,118	660
Accounts receivable, net—third parties	$ 13,535	$ 9,914

Inventories (Details)

Inventories (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Inventory Disclosure [Abstract]
Finished products	$ 1,532	$ 2,154
Feedstock, additives and chemicals	468	330
Inventories	$ 2,000	$ 2,484

Property, Plant and Equipment (

Property, Plant and Equipment (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Property, Plant and Equipment [Abstract]
Depreciation expense on property, plant and equipment	$ 22,753	$ 22,214

Deferred Charges and Other As_2

Deferred Charges and Other Assets (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Deferred Charges and Other Assets [Member]
Other Assets [Line Items]
Amortization expense	$ 3,278	$ 4,630

Distributions and Net Income _3

Distributions and Net Income Per Limited Partner Unit (Distributions Declared) (Details) - USD ($) $ / shares in Units, $ in Thousands	Apr. 30, 2020	Mar. 31, 2020	Mar. 31, 2019
Distribution Made to Limited Partner [Line Items]
Net income in excess of distribution (distribution in excess of net income)		$ 1,156	$ (711)
Net income attributable to the Partnership		$ 17,747	$ 14,955
Weighted Average Number of Limited Partnership and General Partnership Unit Outstanding, Basic and Diluted		35,194,545	32,345,398
Distributions declared		$ 16,591	$ 15,666
IDR Holders [Member]
Distribution Made to Limited Partner [Line Items]
Net income in excess of distribution (distribution in excess of net income)		0	0
Net income attributable to the Partnership		0	0
Distributions declared with respect to the incentive distribution rights		0	0
Common units [Member]
Distribution Made to Limited Partner [Line Items]
Net income in excess of distribution (distribution in excess of net income)		1,156	(711)
Net income attributable to the Partnership		$ 17,747	$ 14,955
Weighted Average Number of Limited Partnership and General Partnership Unit Outstanding, Basic and Diluted		35,194,545	32,345,398
Distributions declared		$ 16,591	$ 15,666
Net Income (Loss), Per Outstanding Limited Partnership Unit, Basic, Net of Tax		$ 0.50	$ 0.46
Cash Distribution [Member] | Common units [Member]
Distribution Made to Limited Partner [Line Items]
Distributions declared		$ 16,591	$ 15,666
Cash Distribution [Member] | Common And Subordinated Units [Member]
Distribution Made to Limited Partner [Line Items]
Incentive Distribution Rights, Target Distribution Per Unit Requiring Marginal Percentage Distribution to IDR Holders		$ 1.2938
Cash Distribution [Member] | Common And Subordinated Units [Member] | Subsequent Event [Member]
Distribution Made to Limited Partner [Line Items]
Distribution declared per unit (in usd per unit)	$ 0.4714
Above $1.2938 up to $1.4063 | Minimum [Member]
Distribution Made to Limited Partner [Line Items]
Incentive Distribution Rights, Target Distribution Per Unit Requiring Marginal Percentage Distribution to IDR Holders		1.2938
Above $1.2938 up to $1.4063 | Maximum [Member]
Distribution Made to Limited Partner [Line Items]
Incentive Distribution Rights, Target Distribution Per Unit Requiring Marginal Percentage Distribution to IDR Holders		$ 1.4063
Above $1.2938 up to $1.4063 | Unit Holders [Member]
Distribution Made to Limited Partner [Line Items]
Incentive Distribution, Marginal Percentage Interest in Distributions		85.00%
Above $1.2938 up to $1.4063 | IDR Holders [Member]
Distribution Made to Limited Partner [Line Items]
Incentive Distribution, Marginal Percentage Interest in Distributions		15.00%
Above $1.4063 up to $1.6875 | Minimum [Member]
Distribution Made to Limited Partner [Line Items]
Incentive Distribution Rights, Target Distribution Per Unit Requiring Marginal Percentage Distribution to IDR Holders		$ 1.4063
Above $1.4063 up to $1.6875 | Maximum [Member]
Distribution Made to Limited Partner [Line Items]
Incentive Distribution Rights, Target Distribution Per Unit Requiring Marginal Percentage Distribution to IDR Holders		$ 1.6875
Above $1.4063 up to $1.6875 | Unit Holders [Member]
Distribution Made to Limited Partner [Line Items]
Incentive Distribution, Marginal Percentage Interest in Distributions		75.00%
Above $1.4063 up to $1.6875 | IDR Holders [Member]
Distribution Made to Limited Partner [Line Items]
Incentive Distribution, Marginal Percentage Interest in Distributions		25.00%
Above $1.6875 | Minimum [Member]
Distribution Made to Limited Partner [Line Items]
Incentive Distribution Rights, Target Distribution Per Unit Requiring Marginal Percentage Distribution to IDR Holders		$ 1.6875
Above $1.6875 | Unit Holders [Member]
Distribution Made to Limited Partner [Line Items]
Incentive Distribution, Marginal Percentage Interest in Distributions		50.00%
Above $1.6875 | IDR Holders [Member]
Distribution Made to Limited Partner [Line Items]
Incentive Distribution, Marginal Percentage Interest in Distributions		50.00%

Distributions and Net Income _4

Distributions and Net Income Per Limited Partner Unit (Income In Excess Of Distribution) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Net income attributable to the Partnership	$ 17,747	$ 14,955
Distributions declared	16,591	15,666
Net income in excess of distribution (distribution in excess of net income)	1,156	(711)
IDR Holders [Member]
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Net income attributable to the Partnership	0	0
Distributions declared with respect to the incentive distribution rights	0	0
Net income in excess of distribution (distribution in excess of net income)	0	0
Common units [Member]
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Net income attributable to the Partnership	17,747	14,955
Distributions declared	16,591	15,666
Net income in excess of distribution (distribution in excess of net income)	1,156	(711)
Cash Distribution [Member] | Common units [Member]
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Distributions declared	$ 16,591	$ 15,666

Distributions and Net Income _5

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
	Mar. 31, 2020	Mar. 31, 2019
Limited Partners' Capital Account [Line Items]
Distributions declared	$ 16,591	$ 15,666
Net income in excess of distribution (distribution in excess of net income)	1,156	(711)
Net income	$ 17,747	$ 14,955
Weighted Average Number of Limited Partnership and General Partnership Unit Outstanding, Basic and Diluted	35,194,545	32,345,398
Common units [Member]
Limited Partners' Capital Account [Line Items]
Distributions declared	$ 16,591	$ 15,666
Net income in excess of distribution (distribution in excess of net income)	1,156	(711)
Net income	$ 17,747	$ 14,955
Weighted Average Number of Limited Partnership and General Partnership Unit Outstanding, Basic and Diluted	35,194,545	32,345,398
Weighted average units outsanding:
Net Income (Loss), Per Outstanding Limited Partnership Unit, Basic, Net of Tax	$ 0.50	$ 0.46
IDR Holders [Member]
Limited Partners' Capital Account [Line Items]
Subsequent distribution to IDR holders	$ 0	$ 0
Net income in excess of distribution (distribution in excess of net income)	0	0
Net income	$ 0	$ 0

Distributions and Net Income _6

Distributions and Net Income Per Limited Partner Unit (Distribution Per Common Unit) (Details) - $ / shares	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Distribution Per Common Unit [Abstract]
Distribution Made to Limited Partner, Distributions Paid, Per Unit	$ 0.4714	$ 0.4328

Partners' Equity (Details)

Partners' Equity (Details) - USD ($) $ / shares in Units, $ in Thousands	Mar. 29, 2019	Oct. 04, 2018	Aug. 04, 2014	Mar. 31, 2020	Mar. 31, 2019
Class of Stock [Line Items]
Partners Units, Maximum Aggregate Offering Amount, ATM		$ 50
Net proceeds from private placement of common units	$ 62,934			$ 0	$ 62,934
Limited Partner [Member]
Class of Stock [Line Items]
Number of units sold in public offering	2,940,818		12,937,500
Units sold in secondary offering price per unit (in dollars per share)	$ 21.40
Affiliated Entity [Member]
Class of Stock [Line Items]
Partners' Capital Account, Units, Sold to Related Party	1,401,869

Related Party Transactions (Sal

Related Party Transactions (Sales to Related Parties) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Related Party Transactions [Abstract]
Revenue from Related Parties	$ 214,828	$ 257,040

Related Party Transactions (Cos

Related Party Transactions (Cost of Sales from Related Parties) (Details) - Affiliated Entity [Member] - Westlake [Member] - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Related Party Transaction [Line Items]
Charges from related parties in cost of sales	$ 83,738	$ 149,727
Feedstock purchased [Member]
Related Party Transaction [Line Items]
Charges from related parties in cost of sales	59,638	122,155
Other service charges [Member]
Related Party Transaction [Line Items]
Charges from related parties in cost of sales	$ 24,100	$ 27,572

Related Party Transactions (Ser

Related Party Transactions (Services from Related Parties Included in SG&A Expenses) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Affiliated Entity [Member] | Westlake [Member]
Related Party Transaction [Line Items]
Services received from Westlake and included in selling, general and administrative expenses	$ 5,115	$ 6,603

Related Party Transactions (Goo

Related Party Transactions (Goods and Services Purchased from Westlake and Capitalized as Assets) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Affiliated Entity [Member] | Westlake [Member]
Related Party Transaction [Line Items]
Goods and services purchased from Westlake and capitalized as assets	$ 480	$ 643

Related Party Transactions (Acc

Related Party Transactions (Accounts Receivable from and Accounts Payable to Related Parties) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Related Party Transaction [Line Items]
Receivable under the Investment Management Agreement—Westlake Chemical Corporation (Westlake)	$ 161,759	$ 162,773
Accounts payable—Westlake	4,333	15,201
Affiliated Entity [Member] | Westlake [Member]
Related Party Transaction [Line Items]
Accounts receivable—Westlake, current and non-current	$ 40,560	$ 42,847

Related Party Transactions (Gen

Related Party Transactions (General) (Details) - Affiliated Entity [Member] - Westlake [Member] - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Related Party Transaction [Line Items]
Operating Lease, Expense	$ 670	$ 514
Interest earned related to the IMA	587	$ 818
Accrued Liabilities [Member]
Related Party Transaction [Line Items]
Accrued interest included in receivable under IMA	$ 587		$ 601

Related Party Transactions (Deb

Related Party Transactions (Debt Payable to Related Parties) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Related Party Transaction [Line Items]
Interest on related party debt payable	$ 3,950	$ 5,900
Accrued interest on related party debt	3,950		$ 4,187
Long-term debt payable to Westlake	399,674		399,674
Affiliated Entity [Member] | Westlake [Member]
Related Party Transaction [Line Items]
Interest capitalized	0
Other income (expense) [Member] | Affiliated Entity [Member] | Westlake [Member]
Related Party Transaction [Line Items]
Interest on related party debt payable	3,950	$ 5,900
Accrued Liabilities [Member] | Affiliated Entity [Member] | Westlake [Member]
Related Party Transaction [Line Items]
Accrued interest on related party debt	$ 3,950		$ 4,187

Related Party Transactions (Sit

Related Party Transactions (Site Lease Agreements) (Details)	3 Months Ended
	Mar. 31, 2020USD ($)
Related Party Transaction [Line Items]
Site lease agreement, number	2
Site lease agreements, term (in years)	50
Site lease agreements, OpCo annual obligation to WLK	$ 1

Related Party Transactions (Maj

Related Party Transactions (Major Customer and Concentration Risk) (Details)	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Affiliated Entity [Member] | Westlake [Member] | Revenue Benchmark [Member] | Customer Concentration Risk [Member]
Concentration Risk [Line Items]
Concentration Risk, Percentage	85.70%	85.90%

Long-term Debt Payable to Wes_3

Long-term Debt Payable to Westlake (Details) - USD ($) $ in Thousands	Mar. 29, 2019	Apr. 30, 2019	Mar. 31, 2020	Dec. 31, 2019
Related Party Transaction [Line Items]
Long-term debt payable to Westlake			$ 399,674	$ 399,674
Repayments of debt		$ 201,445
Weighted average interest rate			3.90%	4.10%
Limited Partner [Member] | OpCo Revolver [Member] | Senior Unsecured Revolving Credit Facility [Member]
Related Party Transaction [Line Items]
Long-term debt payable to Westlake			$ 22,619	$ 22,619
Limited Partner [Member] | OpCo Revolver [Member] | Senior Unsecured Revolving Credit Facility [Member] | LIBOR [Member]
Related Party Transaction [Line Items]
Basis spread on variable rate, percent			2.00%	2.00%
Limited Partner [Member] | MLP Revolver [Member] | Senior Unsecured Revolving Credit Facility [Member]
Related Party Transaction [Line Items]
Long-term debt payable to Westlake			$ 377,055	$ 377,055
Limited Partner [Member] | MLP Revolver [Member] | Senior Unsecured Revolving Credit Facility [Member] | LIBOR [Member]
Related Party Transaction [Line Items]
Basis spread on variable rate, percent			2.00%	2.00%
Westlake Chemical OpCo LP [Member] | Affiliated Entity [Member]
Related Party Transaction [Line Items]
Proceeds from debt payable to Westlake	$ 123,512		$ 0
Limited partner interest, additional ownership	4.50%
Westlake Chemical OpCo LP [Member] | Affiliated Entity [Member] | LIBOR [Member]
Related Party Transaction [Line Items]
Basis spread on variable rate, percent	2.00%
Westlake Chemical OpCo LP [Member] | Affiliated Entity [Member] | Alternate Base Rate [Domain]
Related Party Transaction [Line Items]
Basis spread on variable rate, percent	1.00%

Derivative Commodity Instrume_2

Derivative Commodity Instruments (Details) $ in Thousands, lb in Millions, gal in Millions	Mar. 31, 2020USD ($)lbgal	Dec. 31, 2019USD ($)lbgal	Mar. 31, 2020USD ($)	Mar. 31, 2019USD ($)
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Volume | gal	22.7	39.1
Derivative, Nonmonetary Notional Amount, Mass | lb	54	93
Derivative Liability, Current	$ 1,708	$ 1,959	$ 1,708
Derivative Asset, Current	$ 2,838	$ 597	2,838
Sales [Member]
Derivative [Line Items]
Gain on derivative instruments			3,354	$ 2,211
Cost of Sales [Member]
Derivative [Line Items]
Loss on derivative instruments			$ (1,448)	$ (880)

Fair Value Measurements (Summar

Fair Value Measurements (Summary of Carrying and Fair Values of Long Term Debt) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt payable to Westlake, carrying value	$ 399,674	$ 399,674
OpCo Revolver [Member] | Senior Unsecured Revolving Credit Facility [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt payable to Westlake, fair value	20,864	23,364
OpCo Revolver [Member] | Senior Unsecured Revolving Credit Facility [Member] | Limited Partner [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt payable to Westlake, carrying value	22,619	22,619
MLP Revolver [Member] | Senior Unsecured Revolving Credit Facility [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt payable to Westlake, fair value	380,737	379,452
MLP Revolver [Member] | Senior Unsecured Revolving Credit Facility [Member] | Limited Partner [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt payable to Westlake, carrying value	$ 377,055	$ 377,055

Supplemental Information (Detai

Supplemental Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Accrued Liabilities [Abstract]
Accrued and other liabilities	$ 18,032		$ 17,507
Accrued interest	3,950		4,187
Accrued taxes	3,536		2,611
Accrued maintenance	3,769		3,225
Derivative trading accrual	1,708		1,959
Accrued capital expenditures	1,630		$ 2,375
Increase (reduction) in capital expenditure accrual	$ 20	$ 52