Westlake Chemical Partners (WLKP) 10-Q 3 Nov 21 2021 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2021	Oct. 27, 2021
Document Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2021
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		35,214,416
Amendment Flag	false
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q3
Current Fiscal Year End Date	--12-31
Entity Central Index Key	0001604665

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Current assets
Cash and cash equivalents	$ 18,647	$ 17,154
Receivable under the Investment Management Agreement—Westlake Chemical Corporation ("Westlake")	196,252	123,228
Accounts receivable, net—Westlake	57,020	108,028
Accounts receivable, net—third parties	12,168	11,029
Inventories	6,590	3,474
Prepaid expenses and other current assets	566	392
Total current assets	291,243	263,305
Property, plant and equipment, net	1,022,181	1,050,677
Goodwill	5,814	5,814
Deferred charges and other assets, net	41,324	36,692
Total assets	1,360,562	1,356,488
Current liabilities
Accounts payable—Westlake	13,259	7,855
Accounts payable—third parties	16,773	13,131
Accrued and other liabilities	24,527	18,768
Total current liabilities	54,559	39,754
Long-term debt payable to Westlake	399,674	399,674
Deferred income taxes	1,510	1,542
Other liabilities	0	381
Total liabilities	455,743	441,351
Commitments and contingencies (Note 12)
EQUITY
Total Westlake Chemical Partners LP partners' capital	281,066	277,399
Noncontrolling interest in Westlake Chemical OpCo LP ("OpCo")	623,753	637,738
Total equity	904,819	915,137
Total liabilities and equity	1,360,562	1,356,488
Limited Partner | Common units | Publicly and Privately Held
EQUITY
Limited Partners' Capital Account	474,062	471,701
Total equity	474,062	471,701
Limited Partner | Common units | Westlake
EQUITY
Limited Partners' Capital Account	49,576	48,270
Total equity	49,576	48,270
General Partner | Westlake
EQUITY
General partner—Westlake	(242,572)	(242,572)
Total equity	$ (242,572)	$ (242,572)

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - Common units - shares	Sep. 30, 2021	Dec. 31, 2020
Publicly and Privately Held
Units issued	21,092,186	21,076,673
Westlake
Units issued	14,122,230	14,122,230

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Net sales—Westlake	$ 247,887	$ 217,763	$ 708,646	$ 660,022
Net co-product, ethylene and other sales—third parties	46,079	14,206	175,756	60,996
Total net sales	293,966	231,969	884,402	721,018
Cost of sales	218,038	131,578	589,746	427,049
Gross profit	75,928	100,391	294,656	293,969
Selling, general and administrative expenses	7,792	6,255	24,734	18,590
Income from operations	68,136	94,136	269,922	275,379
Other income (expense)
Interest expense—Westlake	(2,190)	(2,320)	(6,650)	(9,701)
Other income, net	24	17	52	725
Income before income taxes	65,970	91,833	263,324	266,403
Income tax provision (benefit)	(105)	(15)	333	408
Net income	66,075	91,848	262,991	265,995
Less: Net income attributable to noncontrolling interest in OpCo	53,285	73,313	209,956	214,853
Net income attributable to Westlake Chemical Partners LP and limited partners' interest in net income	$ 12,790	$ 18,535	$ 53,035	$ 51,142
Net income per limited partner unit attributable to Westlake Chemical Partners LP per limited partner unit (basic and diluted)
Weighted average limited partner units outstanding (basic and diluted) (in units)	35,209,976	35,194,545	35,203,609	35,194,545
Common units
Other income (expense)
Net income attributable to Westlake Chemical Partners LP and limited partners' interest in net income	$ 12,790	$ 18,535	$ 53,035	$ 51,142
Net income per limited partner unit attributable to Westlake Chemical Partners LP per limited partner unit (basic and diluted)
Common units (in usd per share)	$ 0.36	$ 0.53	$ 1.51	$ 1.45
Weighted average limited partner units outstanding (basic and diluted) (in units)	35,209,976	35,194,545	35,203,609	35,194,545
Common units | Westlake
Net income per limited partner unit attributable to Westlake Chemical Partners LP per limited partner unit (basic and diluted)
Weighted average limited partner units outstanding (basic and diluted) (in units)	14,122,230	14,122,230	14,122,230	14,122,230
Common units | Publicly and Privately Held
Net income per limited partner unit attributable to Westlake Chemical Partners LP per limited partner unit (basic and diluted)
Weighted average limited partner units outstanding (basic and diluted) (in units)	21,087,746	21,072,315	21,081,379	21,072,315

Consolidated Statements of Chan

Consolidated Statements of Changes in Equity - USD ($) $ in Thousands	Total	Noncontrolling Interest in OpCo	WestlakeGeneral Partner	Common unitsPublicly and Privately HeldLimited Partner	Common unitsWestlakeLimited Partner
Total equity at Dec. 31, 2019	$ 952,135	$ 674,621	$ (242,572)	$ 471,736	$ 48,350
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	93,770	76,023		10,626	7,121
Quarterly distribution to unitholders	(16,591)			(9,934)	(6,657)
Quarterly distribution to noncontrolling interest retained in OpCo by Westlake	(79,223)	(79,223)
Total equity at Mar. 31, 2020	950,091	671,421	(242,572)	472,428	48,814
Total equity at Dec. 31, 2019	952,135	674,621	(242,572)	471,736	48,350
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	265,995
Total equity at Sep. 30, 2020	938,832	659,948	(242,572)	472,556	48,900
Total equity at Mar. 31, 2020	950,091	671,421	(242,572)	472,428	48,814
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	80,377	65,517		8,897	5,963
Quarterly distribution to unitholders	(16,590)			(9,933)	(6,657)
Quarterly distribution to noncontrolling interest retained in OpCo by Westlake	(78,025)	(78,025)
Total equity at Jun. 30, 2020	935,853	658,913	(242,572)	471,392	48,120
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	91,848	73,313		11,098	7,437
Quarterly distribution to unitholders	(16,591)			(9,934)	(6,657)
Quarterly distribution to noncontrolling interest retained in OpCo by Westlake	(72,278)	(72,278)
Total equity at Sep. 30, 2020	938,832	659,948	(242,572)	472,556	48,900
Total equity at Dec. 31, 2020	915,137	637,738	(242,572)	471,701	48,270
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	76,622	61,476		9,069	6,077
Quarterly distribution to unitholders	(16,593)			(9,936)	(6,657)
Quarterly distribution to noncontrolling interest retained in OpCo by Westlake	(62,058)	(62,058)
Total equity at Mar. 31, 2021	913,108	637,156	(242,572)	470,834	47,690
Total equity at Dec. 31, 2020	915,137	637,738	(242,572)	471,701	48,270
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	262,991
Total equity at Sep. 30, 2021	904,819	623,753	(242,572)	474,062	49,576
Total equity at Mar. 31, 2021	913,108	637,156	(242,572)	470,834	47,690
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	120,294	95,195		15,029	10,070
Units issued for vested phantom units	149			149
Quarterly distribution to unitholders	(16,593)			(9,936)	(6,657)
Quarterly distribution to noncontrolling interest retained in OpCo by Westlake	(65,200)	(65,200)
Total equity at Jun. 30, 2021	951,758	667,151	(242,572)	476,076	51,103
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	66,075	53,285		7,660	5,130
Units issued for vested phantom units	262			262
Quarterly distribution to unitholders	(16,593)			(9,936)	(6,657)
Quarterly distribution to noncontrolling interest retained in OpCo by Westlake	(96,683)	(96,683)
Total equity at Sep. 30, 2021	$ 904,819	$ 623,753	$ (242,572)	$ 474,062	$ 49,576

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Cash flows from operating activities
Net income	$ 262,991	$ 265,995
Adjustments to reconcile net income to net cash provided by operating activities
Depreciation and amortization	82,830	77,767
Loss from disposition of property, plant and equipment	1,763	1,000
Other gains, net	866	(522)
Changes in operating assets and liabilities
Accounts receivable—third parties	(2,037)	5,170
Net accounts receivable—Westlake	56,228	(10,136)
Inventories	(3,116)	832
Prepaid expenses and other current assets	(174)	(87)
Accounts payable	2,689	711
Accrued and other liabilities	3,690	1,398
Other, net	(19,153)	(1,252)
Cash flows from investing activities	386,577	340,876
Cash flows from investing activities
Additions to property, plant and equipment	(38,490)	(29,170)
Maturities of investments with Westlake under the Investment Management Agreement	203,000	276,000
Investments with Westlake under the Investment Management Agreement	(276,000)	(305,000)
Other	126	0
Net cash used for investing activities	(111,364)	(58,170)
Cash flows from financing activities
Quarterly distributions to noncontrolling interest retained in OpCo by Westlake	(223,941)	(229,526)
Quarterly distributions to unitholders	(49,779)	(49,772)
Net cash used for financing activities	(273,720)	(279,298)
Net increase in cash and cash equivalents	1,493	3,408
Cash and cash equivalents at beginning of period	17,154	19,923
Cash and cash equivalents at end of period	$ 18,647	$ 23,331

Description of Business and Bas

Description of Business and Basis of Presentation	9 Months Ended
	Sep. 30, 2021
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% limited partner 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 (collectively, the "Contributed Assets" ) . Since the IPO, the Partnership has periodically purchased additional limited partner interest in OpCo. Most recently, 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, 2020 (the "2020 Form 10-K"), filed with the SEC on March 2, 2021. 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, 2020. 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 September 30, 2021, its results of operations for the three and nine months ended September 30, 2021 and 2020 and the changes in its cash position for the nine months ended September 30, 2021 and 2020. 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, 2021 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. The COVID pandemic resulted in widespread adverse impacts on the global economy in 2020. The Partnership has not experienced significant disruptions to its business operations in 2020 or during the nine months ended September 30, 2021 and does not expect significant disruptions to its business operations resulting from COVID-19. However, the impact that COVID-19 will have on the Partnership's financial condition, results of operations and cash flows cannot be estimated with certainty at this time as it will depend on future developments, including, among others, the timing and logistics with respect to the distribution of vaccines globally and the efficacy of the available vaccines (including with respect to the more recent variants of COVID-19) and other treatments, the ultimate duration of the pandemic, geographic spread and severity of the virus, the consequences of governmental and other measures designed to prevent the spread of the virus, the impact on the operation of OpCo's facilities, Westlake, customers, suppliers and other third parties and the timing and extent to which normal economic and operating conditions resume. 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 and are not expected to have a material impact on the Partnership's consolidated financial position, results of operations and cash flows. Certain exceptions provided under this guidance may be applicable to future reference rate reform related transitions.

Accounts Receivable - Third Par

Accounts Receivable - Third Parties	9 Months Ended
	Sep. 30, 2021
Accounts Receivable, after Allowance for Credit Loss [Abstract]
Accounts Receivable - Third Parties	Accounts Receivable—Third Parties Accounts receivable—third parties consist of the following: September 30, December 31, Trade customers $ 13,381 $ 11,344 Allowance for credit losses (1,213) (315) Accounts receivable, net—third parties $ 12,168 $ 11,029

Inventories

Inventories	9 Months Ended
	Sep. 30, 2021
Inventory Disclosure [Abstract]
Inventories	Inventories Inventories consist of the following: September 30, December 31, Finished products $ 6,217 $ 3,157 Feedstock, additives and chemicals 373 317 Inventories $ 6,590 $ 3,474

Property, Plant and Equipment

Property, Plant and Equipment	9 Months Ended
	Sep. 30, 2021
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment	Property, Plant and Equipment Depreciation expense on property, plant and equipment of $23,010 and $22,913 is included in cost of sales in the consolidated statements of operations for the three months ended September 30, 2021 and 2020, respectively. Depreciation expense on property, plant and equipment of $68,795 and $68,380 is included in cost of sales in the consolidated statements of operations for the nine months ended September 30, 2021 and 2020, respectively.

Deferred Charges and Other Asse

Deferred Charges and Other Assets	9 Months Ended
	Sep. 30, 2021
Other Assets, Noncurrent [Abstract]
Deferred Charges and Other Assets	Deferred Charges and Other Assets Amortization expense on other assets of $3,576 and $3,010 is included in costs of sales in the consolidated statements of operations for the three months ended September 30, 2021 and 2020, respectively. Amortization expense on other assets of $14,035 and $9,387 is included in costs of sales in the consolidated statements of operations for the nine months ended September 30, 2021 and 2020, respectively.

Distributions and Net Income Pe

Distributions and Net Income Per Limited Partner Unit	9 Months Ended
	Sep. 30, 2021
Earnings Per Share [Abstract]
Distributions and Net Income Per Limited Partner Unit	Distributions and Net Income Per Limited Partner Unit On November 1, 2021, 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 September 30, 2021 of $0.4714 per unit. This distribution is payable on November 29, 2021 to unitholders of record as of November 12, 2021. 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 September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Net income attributable to the Partnership $ 12,790 $ 18,535 $ 53,035 $ 51,142 Less: Limited partners' distribution declared on common units 16,600 16,591 49,788 49,772 Net income in excess of distribution (distribution in excess of net income) $ (3,810) $ 1,944 $ 3,247 $ 1,370 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 September 30, 2021 Limited Partners' Common Units Incentive Distribution Rights Total Net income attributable to the Partnership: Distribution $ 16,600 $ — $ 16,600 Distribution in excess of net income (3,810) — (3,810) Net income $ 12,790 $ — $ 12,790 Weighted average units outstanding: Basic and diluted 35,209,976 35,209,976 Net income per limited partner unit: Basic and diluted $ 0.36 Three Months Ended September 30, 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 1,944 — 1,944 Net income $ 18,535 $ — $ 18,535 Weighted average units outstanding: Basic and diluted 35,194,545 35,194,545 Net income per limited partner unit: Basic and diluted $ 0.53 Nine Months Ended September 30, 2021 Limited Partners' Common Units Incentive Distribution Rights Total Net income attributable to the Partnership: Distribution $ 49,788 $ — $ 49,788 Net income in excess of distribution 3,247 — 3,247 Net income $ 53,035 $ — $ 53,035 Weighted average units outstanding: Basic and diluted 35,203,609 35,203,609 Net income per limited partner unit: Basic and diluted $ 1.51 Nine Months Ended September 30, 2020 Limited Partners' Common Units Incentive Distribution Rights Total Net income attributable to the Partnership: Distribution $ 49,772 $ — $ 49,772 Net income in excess of distribution 1,370 — 1,370 Net income $ 51,142 $ — $ 51,142 Weighted average units outstanding: Basic and diluted 35,194,545 35,194,545 Net income per limited partner unit: Basic and diluted $ 1.45 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 September 30, 2021 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 and nine months ended September 30, 2021 and 2020 were as follows: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Distributions per common unit $ 0.4714 $ 0.4714 $ 1.4142 $ 1.4142

Partners' Equity

Partners' Equity	9 Months Ended
	Sep. 30, 2021
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 September 30, 2021. 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. 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	9 Months Ended
	Sep. 30, 2021
Related Party Transactions [Abstract]
Related Party Transactions	8. 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 September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Net sales—Westlake $ 247,887 $ 217,763 $ 708,646 $ 660,022 OpCo declared force majeure events in September 2021 during the Petro 2 facility turnaround, in June 2021 related to OpCo's Petro 1 facility outage, and in February 2021 due to the severe winter storm. As a result of these events, the Partnership updated its estimate of OpCo's 2021 anticipated production as of September 30, 2021. The buyer deficiency fee is measured based upon the lower of the actual production deficiency at period end or the estimated annual production deficiency based upon OpCo's annual anticipated production. Based upon this change in estimate of OpCo's 2021 anticipated production, the Partnership has recognized buyer deficiency fees and shortfall fees of $3,045 and $21,465 during the three and nine months ended September 30, 2021, respectively. The buyer deficiency fees and shortfall fees are classified as a component of net sales. During 2020, the Lake Charles Petro 1 and Petro 2 facilities were impacted by Hurricanes Laura and Delta, which resulted in force majeure events under the Ethylene Sales Agreement. As a result of the force majeure events, the Partnership recognized a buyer deficiency fee of $69,555 as a component of net sales in 2020. Payment for the buyer deficiency fee was received by the Partnership in January 2021. 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 September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Feedstock purchased from Westlake and included in cost of sales $ 119,000 $ 60,646 $ 302,095 $ 189,608 Other charges from Westlake and included in cost of sales 35,615 23,166 94,923 71,164 Total $ 154,615 $ 83,812 $ 397,018 $ 260,772 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 September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Services received from Westlake and included in selling, general and administrative expenses $ 6,925 $ 5,679 $ 21,837 $ 16,492 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 September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Goods and services purchased from Westlake and capitalized as assets $ 3,606 $ 404 $ 4,542 $ 1,268 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's 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 $81 and $56 was included in the receivable under the Investment Management Agreement balance at September 30, 2021 and December 31, 2020, respectively. Total interest earned related to the Investment Management Agreement was $81 and $69 for the three months ended September 30, 2021 and 2020, respectively, and $225 and $876 for the nine months ended September 30, 2021 and 2020, respectively. The Partnership's receivable under the Investment Management Agreement was as follows: September 30, December 31, Receivable under the Investment Management Agreement $ 196,252 $ 123,228 Accounts Receivable from Related Parties The Partnership's accounts receivable from Westlake result primarily from ethylene sales to Westlake and the buyer deficiency fee and shortfall fee recognized under the Ethylene Sales Agreement, as discussed above under "Sales to Related Parties." The buyer deficiency fee and shortfall fee recognized in the nine months ended September 30, 2021 are scheduled to be received by the Partnership after the end of 2021. The Partnership's accounts receivable from Westlake were as follows: September 30, December 31, Accounts receivable—Westlake $ 57,020 $ 108,028 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: September 30, December 31, Accounts payable—Westlake $ 13,259 $ 7,855 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 $997 and $407 for the three months ended September 30, 2021 and 2020, respectively, and $2,292 and $1,803 for the nine months ended September 30, 2021 and 2020, 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 September 30, 2021 and 2020 was $2,190 and $2,320, respectively. Interest on related party debt payable balances for the nine months ended September 30, 2021 and 2020 was $6,650 and $9,701, respectively. Interest on related party debt payable is presented as interest expense—Westlake in the consolidated statements of operations. At September 30, 2021 and December 31, 2020, accrued interest on related party debt was $2,193 and $2,336, respectively, and is reflected as a component of accrued liabilities in the consolidated balance sheets. Debt payable to related parties was as follows: September 30, December 31, Long-term debt payable to Westlake $ 399,674 $ 399,674 Major Customer and Concentration of Credit Risk During the three months ended September 30, 2021 and 2020, Westlake accounted for approximately 84.3% and 93.9%, respectively, of the Partnership's net sales. During the nine months ended September 30, 2021 and 2020, Westlake accounted for approximately 80.1% and 91.5%, respectively, of the Partnership's net sales.

Long-term Debt Payable to Westl

Long-term Debt Payable to Westlake	9 Months Ended
	Sep. 30, 2021
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: September 30, 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 The weighted average interest rate on all long-term debt was 2.1% and 2.2% at September 30, 2021 and December 31, 2020, respectively. As of September 30, 2021, the Partnership was in compliance with all of the covenants under the OpCo Revolver and the MLP Revolver.

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2021
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 September 30, 2021 and December 31, 2020 are summarized in the table below. The Partnership's long-term debt includes the OpCo Revolver and the MLP Revolver at September 30, 2021. 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. September 30, 2021 December 31, 2020 Carrying Fair Carrying Fair OpCo Revolver $ 22,619 $ 23,410 $ 22,619 $ 23,301 MLP Revolver 377,055 385,426 377,055 383,284

Supplemental Information

Supplemental Information	9 Months Ended
	Sep. 30, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Supplemental Information	Supplemental Information Accrued and Other Liabilities Accrued and other liabilities were $24,527 and $18,768 at September 30, 2021 and December 31, 2020, respectively. Accrued taxes, accrued maintenance expense, accrued turnaround costs and accrued capital expenditures, which are components of accrued liabilities, were $4,784, $5,438, $3,330 and $4,832, respectively, at September 30, 2021 and $6,207, $3,905, $0 and $2,286, respectively, at December 31, 2020. No other component of accrued and other 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 $3,663 and $1,945 for the nine months ended September 30, 2021 and 2020, respectively.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2021
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. On September 27, 2021, shortly after the turnaround on Petro 2 commenced, there was a flash fire at the quench tower of the Petro 2 facility. Several contractors working on the quench tower were injured. There are five lawsuits pending in connection with the flash fire. The Partnership is also involved in other 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.

Description of Business and B_2

Description of Business and Basis of Presentation (Policies)	9 Months Ended
	Sep. 30, 2021
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, 2020 (the "2020 Form 10-K"), filed with the SEC on March 2, 2021. 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, 2020. 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 September 30, 2021, its results of operations for the three and nine months ended September 30, 2021 and 2020 and the changes in its cash position for the nine months ended September 30, 2021 and 2020. 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, 2021 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. The COVID pandemic resulted in widespread adverse impacts on the global economy in 2020. The Partnership has not experienced significant disruptions to its business operations in 2020 or during the nine months ended September 30, 2021 and does not expect significant disruptions to its business operations resulting from COVID-19. However, the impact that COVID-19 will have on the Partnership's financial condition, results of operations and cash flows cannot be estimated with certainty at this time as it will depend on future developments, including, among others, the timing and logistics with respect to the distribution of vaccines globally and the efficacy of the available vaccines (including with respect to the more recent variants of COVID-19) and other treatments, the ultimate duration of the pandemic, geographic spread and severity of the virus, the consequences of governmental and other measures designed to prevent the spread of the virus, the impact on the operation of OpCo's facilities, Westlake, customers, suppliers and other third parties and the timing and extent to which normal economic and operating conditions resume.
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 and are not expected to have a material impact on the Partnership's consolidated financial position, results of operations and cash flows. Certain exceptions provided under this guidance may be applicable to future reference rate reform related transitions.

Accounts Receivable - Third P_2

Accounts Receivable - Third Parties (Tables)	9 Months Ended
	Sep. 30, 2021
Accounts Receivable, after Allowance for Credit Loss [Abstract]
Schedule Of Accounts Receivable - Third Parties	Accounts receivable—third parties consist of the following: September 30, December 31, Trade customers $ 13,381 $ 11,344 Allowance for credit losses (1,213) (315) Accounts receivable, net—third parties $ 12,168 $ 11,029

Inventories (Tables)

Inventories (Tables)	9 Months Ended
	Sep. 30, 2021
Inventory Disclosure [Abstract]
Schedule Of Inventory	Inventories consist of the following: September 30, December 31, Finished products $ 6,217 $ 3,157 Feedstock, additives and chemicals 373 317 Inventories $ 6,590 $ 3,474

Distributions and Net Income _2

Distributions and Net Income Per Limited Partner Unit (Tables)	9 Months Ended
	Sep. 30, 2021
Earnings Per Share [Abstract]
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 September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Net income attributable to the Partnership $ 12,790 $ 18,535 $ 53,035 $ 51,142 Less: Limited partners' distribution declared on common units 16,600 16,591 49,788 49,772 Net income in excess of distribution (distribution in excess of net income) $ (3,810) $ 1,944 $ 3,247 $ 1,370
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 September 30, 2021 Limited Partners' Common Units Incentive Distribution Rights Total Net income attributable to the Partnership: Distribution $ 16,600 $ — $ 16,600 Distribution in excess of net income (3,810) — (3,810) Net income $ 12,790 $ — $ 12,790 Weighted average units outstanding: Basic and diluted 35,209,976 35,209,976 Net income per limited partner unit: Basic and diluted $ 0.36 Three Months Ended September 30, 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 1,944 — 1,944 Net income $ 18,535 $ — $ 18,535 Weighted average units outstanding: Basic and diluted 35,194,545 35,194,545 Net income per limited partner unit: Basic and diluted $ 0.53 Nine Months Ended September 30, 2021 Limited Partners' Common Units Incentive Distribution Rights Total Net income attributable to the Partnership: Distribution $ 49,788 $ — $ 49,788 Net income in excess of distribution 3,247 — 3,247 Net income $ 53,035 $ — $ 53,035 Weighted average units outstanding: Basic and diluted 35,203,609 35,203,609 Net income per limited partner unit: Basic and diluted $ 1.51 Nine Months Ended September 30, 2020 Limited Partners' Common Units Incentive Distribution Rights Total Net income attributable to the Partnership: Distribution $ 49,772 $ — $ 49,772 Net income in excess of distribution 1,370 — 1,370 Net income $ 51,142 $ — $ 51,142 Weighted average units outstanding: Basic and diluted 35,194,545 35,194,545 Net income per limited partner unit: Basic and diluted $ 1.45
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 September 30, 2021 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 and nine months ended September 30, 2021 and 2020 were as follows: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Distributions per common unit $ 0.4714 $ 0.4714 $ 1.4142 $ 1.4142

Related Party Transactions (Tab

Related Party Transactions (Tables)	9 Months Ended
	Sep. 30, 2021
Related Party Transactions [Abstract]
Schedule of Related Party Transactions	Sales to related parties were as follows: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Net sales—Westlake $ 247,887 $ 217,763 $ 708,646 $ 660,022 Charges from related parties in cost of sales were as follows: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Feedstock purchased from Westlake and included in cost of sales $ 119,000 $ 60,646 $ 302,095 $ 189,608 Other charges from Westlake and included in cost of sales 35,615 23,166 94,923 71,164 Total $ 154,615 $ 83,812 $ 397,018 $ 260,772 Charges from related parties included within selling, general and administrative expenses were as follows: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Services received from Westlake and included in selling, general and administrative expenses $ 6,925 $ 5,679 $ 21,837 $ 16,492 Charges from related parties for goods and services capitalized as assets were as follows: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Goods and services purchased from Westlake and capitalized as assets $ 3,606 $ 404 $ 4,542 $ 1,268 The Partnership's receivable under the Investment Management Agreement was as follows: September 30, December 31, Receivable under the Investment Management Agreement $ 196,252 $ 123,228 The Partnership's accounts receivable from Westlake were as follows: September 30, December 31, Accounts receivable—Westlake $ 57,020 $ 108,028 The related party accounts payable balances were as follows: September 30, December 31, Accounts payable—Westlake $ 13,259 $ 7,855 Debt payable to related parties was as follows: September 30, December 31, Long-term debt payable to Westlake $ 399,674 $ 399,674

Long-term Debt Payable to Wes_2

Long-term Debt Payable to Westlake (Tables)	9 Months Ended
	Sep. 30, 2021
Related Party Transactions [Abstract]
Related Party Transactions, Long-term Debt	Long-term debt payable to Westlake consists of the following: September 30, 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)	9 Months Ended
	Sep. 30, 2021
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 September 30, 2021 and December 31, 2020 are summarized in the table below. The Partnership's long-term debt includes the OpCo Revolver and the MLP Revolver at September 30, 2021. 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. September 30, 2021 December 31, 2020 Carrying Fair Carrying Fair OpCo Revolver $ 22,619 $ 23,410 $ 22,619 $ 23,301 MLP Revolver 377,055 385,426 377,055 383,284

Description of Business and B_3

Description of Business and Basis of Presentation (Details) - USD ($) $ / shares in Units, $ in Thousands	Mar. 29, 2019	Aug. 04, 2014
Limited Partner
Limited Partners' Capital Account [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
Westlake Chemical OpCo GP LLC | Limited Liability Company
Limited Partners' Capital Account [Line Items]
Limited partner interest		100.00%
Westlake Chemical OpCo LP | Affiliated Entity
Limited Partners' Capital Account [Line Items]
Limited partner interest	22.80%	10.60%
Limited partner interest, additional ownership	4.50%
Amount paid to purchase additional limited partner interest	$ 201,445
Westlake Chemical OpCo LP | Westlake | Majority-Owned Subsidiary, Unconsolidated
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	Sep. 30, 2021	Dec. 31, 2020
Accounts Receivable, after Allowance for Credit Loss [Abstract]
Trade customers	$ 13,381	$ 11,344
Allowance for credit losses	(1,213)	(315)
Accounts receivable, net—third parties	$ 12,168	$ 11,029

Inventories (Details)

Inventories (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Inventory Disclosure [Abstract]
Finished products	$ 6,217	$ 3,157
Feedstock, additives and chemicals	373	317
Inventories	$ 6,590	$ 3,474

Property, Plant and Equipment (

Property, Plant and Equipment (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Property, Plant and Equipment [Abstract]
Depreciation expense on property, plant and equipment	$ 23,010	$ 22,913	$ 68,795	$ 68,380

Deferred Charges and Other As_2

Deferred Charges and Other Assets (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Deferred Charges and Other Assets
Other Assets [Line Items]
Amortization expense	$ 3,576	$ 3,010	$ 14,035	$ 9,387

Distributions and Net Income _3

Distributions and Net Income Per Limited Partner Unit (Distributions Declared) (Details) - USD ($) $ / shares in Units, $ in Thousands	Nov. 01, 2021	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Distribution Made to Limited Partner [Line Items]
Net income in excess of distribution (distribution in excess of net income)		$ (3,810)	$ 1,944	$ 3,247	$ 1,370
Net income attributable to the Partnership		$ 12,790	$ 18,535	$ 53,035	$ 51,142
Weighted average limited partner units outstanding (basic and diluted) (in units)		35,209,976	35,194,545	35,203,609	35,194,545
Distributions declared		$ 16,600	$ 16,591	$ 49,788	$ 49,772
IDR Holders
Distribution Made to Limited Partner [Line Items]
Net income in excess of distribution (distribution in excess of net income)		0	0	0	0
Net income attributable to the Partnership		0	0	0	0
Distributions declared with respect to the incentive distribution rights		0	0	0	0
Common units
Distribution Made to Limited Partner [Line Items]
Net income in excess of distribution (distribution in excess of net income)		(3,810)	1,944	3,247	1,370
Net income attributable to the Partnership		$ 12,790	$ 18,535	$ 53,035	$ 51,142
Weighted average limited partner units outstanding (basic and diluted) (in units)		35,209,976	35,194,545	35,203,609	35,194,545
Distributions declared		$ 16,600	$ 16,591	$ 49,788	$ 49,772
Common units (in usd per share)		$ 0.36	$ 0.53	$ 1.51	$ 1.45
Cash Distribution | Common units
Distribution Made to Limited Partner [Line Items]
Distributions declared		$ 16,600	$ 16,591	$ 49,788	$ 49,772
Cash Distribution | 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 (in usd per share)				$ 1.2938
Cash Distribution | Common And Subordinated Units [Member] | Subsequent Event
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
Distribution Made to Limited Partner [Line Items]
Incentive Distribution Rights, Target Distribution Per Unit Requiring Marginal Percentage Distribution to IDR Holders (in usd per share)				1.2938
Above $1.2938 up to $1.4063 | Maximum
Distribution Made to Limited Partner [Line Items]
Incentive Distribution Rights, Target Distribution Per Unit Requiring Marginal Percentage Distribution to IDR Holders (in usd per share)				$ 1.4063
Above $1.2938 up to $1.4063 | Unit Holders
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
Distribution Made to Limited Partner [Line Items]
Incentive Distribution, Marginal Percentage Interest in Distributions				15.00%
Above $1.4063 up to $1.6875 | Minimum
Distribution Made to Limited Partner [Line Items]
Incentive Distribution Rights, Target Distribution Per Unit Requiring Marginal Percentage Distribution to IDR Holders (in usd per share)				$ 1.4063
Above $1.4063 up to $1.6875 | Maximum
Distribution Made to Limited Partner [Line Items]
Incentive Distribution Rights, Target Distribution Per Unit Requiring Marginal Percentage Distribution to IDR Holders (in usd per share)				$ 1.6875
Above $1.4063 up to $1.6875 | Unit Holders
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
Distribution Made to Limited Partner [Line Items]
Incentive Distribution, Marginal Percentage Interest in Distributions				25.00%
Above $1.6875 | Minimum
Distribution Made to Limited Partner [Line Items]
Incentive Distribution Rights, Target Distribution Per Unit Requiring Marginal Percentage Distribution to IDR Holders (in usd per share)				$ 1.6875
Above $1.6875 | Unit Holders
Distribution Made to Limited Partner [Line Items]
Incentive Distribution, Marginal Percentage Interest in Distributions				50.00%
Above $1.6875 | IDR Holders
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 ($) $ / shares in Units, $ in Thousands	Nov. 01, 2021	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Net income attributable to the Partnership		$ 12,790	$ 18,535	$ 53,035	$ 51,142
Distributions declared		16,600	16,591	49,788	49,772
Net income in excess of distribution (distribution in excess of net income)		$ (3,810)	$ 1,944	$ 3,247	$ 1,370
Distribution Made to Limited Partner, Distributions Paid, Per Unit		$ 0.4714	$ 0.4714	$ 1.4142	$ 1.4142
IDR Holders
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Net income attributable to the Partnership		$ 0	$ 0	$ 0	$ 0
Distributions declared with respect to the incentive distribution rights		0	0	0	0
Net income in excess of distribution (distribution in excess of net income)		0	0	0	0
Common units
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Net income attributable to the Partnership		12,790	18,535	53,035	51,142
Distributions declared		16,600	16,591	49,788	49,772
Net income in excess of distribution (distribution in excess of net income)		(3,810)	1,944	3,247	1,370
Cash Distribution | Common units
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Distributions declared		$ 16,600	$ 16,591	$ 49,788	$ 49,772
Cash Distribution | Common And Subordinated Units [Member] | Subsequent Event
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Distribution declared per unit (in usd per unit)	$ 0.4714

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		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Limited Partners' Capital Account [Line Items]
Distributions declared	$ 16,600	$ 16,591	$ 49,788	$ 49,772
Net income in excess of distribution (distribution in excess of net income)	(3,810)	1,944	3,247	1,370
Net income	$ 12,790	$ 18,535	$ 53,035	$ 51,142
Weighted average limited partner units outstanding (basic and diluted) (in units)	35,209,976	35,194,545	35,203,609	35,194,545
Common units
Limited Partners' Capital Account [Line Items]
Distributions declared	$ 16,600	$ 16,591	$ 49,788	$ 49,772
Net income in excess of distribution (distribution in excess of net income)	(3,810)	1,944	3,247	1,370
Net income	$ 12,790	$ 18,535	$ 53,035	$ 51,142
Weighted average limited partner units outstanding (basic and diluted) (in units)	35,209,976	35,194,545	35,203,609	35,194,545
Weighted average units outsanding:
Common units (in usd per share)	$ 0.36	$ 0.53	$ 1.51	$ 1.45
IDR Holders
Limited Partners' Capital Account [Line Items]
Subsequent distribution to IDR holders	$ 0	$ 0	$ 0	$ 0
Net income in excess of distribution (distribution in excess of net income)	0	0	0	0
Net income	$ 0	$ 0	$ 0	$ 0

Distributions and Net Income _6

Distributions and Net Income Per Limited Partner Unit (Distribution Per Common Unit) (Details) - $ / shares	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Distribution Per Common Unit [Abstract]
Distribution Made to Limited Partner, Distributions Paid, Per Unit	$ 0.4714	$ 0.4714	$ 1.4142	$ 1.4142

Partners' Equity (Details)

Partners' Equity (Details) - USD ($) $ / shares in Units, $ in Thousands	Mar. 29, 2019	Oct. 04, 2018	Aug. 04, 2014
Class of Stock [Line Items]
Partners Units, Maximum Aggregate Offering Amount, ATM		$ 50
Limited Partner
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
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		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Related Party Transaction [Line Items]
Revenue from Related Parties	$ 247,887	$ 217,763	$ 708,646	$ 660,022
Buyer deficiency fee	$ 3,045		$ 21,465		$ 69,555

Related Party Transactions (Cos

Related Party Transactions (Cost of Sales from Related Parties) (Details) - Affiliated Entity - Westlake - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Related Party Transaction [Line Items]
Charges from related parties in cost of sales	$ 154,615	$ 83,812	$ 397,018	$ 260,772
Feedstock Purchased
Related Party Transaction [Line Items]
Charges from related parties in cost of sales	119,000	60,646	302,095	189,608
Other service charges
Related Party Transaction [Line Items]
Charges from related parties in cost of sales	$ 35,615	$ 23,166	$ 94,923	$ 71,164

Related Party Transactions (Ser

Related Party Transactions (Services from Related Parties Included in SG&A Expenses) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Affiliated Entity | Westlake
Related Party Transaction [Line Items]
Services received from Westlake and included in selling, general and administrative expenses	$ 6,925	$ 5,679	$ 21,837	$ 16,492

Related Party Transactions (Goo

Related Party Transactions (Goods and Services Purchased from Westlake and Capitalized as Assets) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Affiliated Entity | Westlake
Related Party Transaction [Line Items]
Goods and services purchased from Westlake and capitalized as assets	$ 3,606	$ 404	$ 4,542	$ 1,268

Related Party Transactions (Acc

Related Party Transactions (Accounts Receivable from and Accounts Payable to Related Parties) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Related Party Transaction [Line Items]
Receivable under the Investment Management Agreement—Westlake Chemical Corporation ("Westlake")	$ 196,252		$ 196,252		$ 123,228
Accounts payable—Westlake	13,259		13,259		7,855
Accounts receivable, net—Westlake	57,020		57,020		$ 108,028
Affiliated Entity | Westlake
Related Party Transaction [Line Items]
Interest earned related to the IMA	$ 81	$ 69	$ 225	$ 876

Related Party Transactions (Gen

Related Party Transactions (General) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Related Party Transaction [Line Items]
Buyer deficiency fee	$ 3,045		$ 21,465		$ 69,555
Affiliated Entity | Westlake
Related Party Transaction [Line Items]
Interest earned related to the IMA	81	$ 69	225	$ 876
Operating lease expense	997	$ 407	2,292	$ 1,803
Accrued Liabilities | Affiliated Entity | Westlake
Related Party Transaction [Line Items]
Accrued interest included in receivable under IMA	$ 81		$ 81		$ 56

Related Party Transactions (Deb

Related Party Transactions (Debt Payable to Related Parties) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Related Party Transaction [Line Items]
Interest on related party debt payable	$ 2,190	$ 2,320	$ 6,650	$ 9,701
Long-term debt payable to Westlake	399,674		399,674		$ 399,674
Other income (expense) | Affiliated Entity | Westlake
Related Party Transaction [Line Items]
Interest on related party debt payable	2,190	$ 2,320	6,650	$ 9,701
Accrued Liabilities | Affiliated Entity | Westlake
Related Party Transaction [Line Items]
Accrued interest on related party debt	$ 2,193		$ 2,193		$ 2,336

Related Party Transactions (Sit

Related Party Transactions (Site Lease Agreements) (Details)	9 Months Ended
	Sep. 30, 2021USD ($)
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		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Affiliated Entity | Westlake | Revenue Benchmark | Customer Concentration Risk
Concentration Risk [Line Items]
Concentration Risk, Percentage	84.30%	93.90%	80.10%	91.50%

Long-term Debt Payable to Wes_3

Long-term Debt Payable to Westlake (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Related Party Transaction [Line Items]
Long-term debt payable to Westlake	$ 399,674	$ 399,674
Weighted average interest rate	2.10%	2.20%
Limited Partner | OpCo Revolver | Senior Unsecured Revolving Credit Facility
Related Party Transaction [Line Items]
Long-term debt payable to Westlake	$ 22,619	$ 22,619
Limited Partner | OpCo Revolver | Senior Unsecured Revolving Credit Facility | LIBOR [Member]
Related Party Transaction [Line Items]
Basis spread on variable rate, percent	2.00%
Limited Partner | MLP Revolver | Senior Unsecured Revolving Credit Facility
Related Party Transaction [Line Items]
Long-term debt payable to Westlake	$ 377,055	$ 377,055
Limited Partner | MLP Revolver | Senior Unsecured Revolving Credit Facility | LIBOR [Member]
Related Party Transaction [Line Items]
Basis spread on variable rate, percent	2.00%

Fair Value Measurements (Summar

Fair Value Measurements (Summary of Carrying and Fair Values of Long Term Debt) (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt payable to Westlake, carrying value	$ 399,674	$ 399,674
OpCo Revolver | Senior Unsecured Revolving Credit Facility
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt payable to Westlake, fair value	23,410	23,301
OpCo Revolver | Senior Unsecured Revolving Credit Facility | Limited Partner
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt payable to Westlake, carrying value	22,619	22,619
MLP Revolver | Senior Unsecured Revolving Credit Facility
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt payable to Westlake, fair value	385,426	383,284
MLP Revolver | Senior Unsecured Revolving Credit Facility | Limited Partner
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	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Accrued Liabilities [Abstract]
Accrued and other liabilities	$ 24,527		$ 18,768
Accrued taxes	4,784		6,207
Accrued maintenance	5,438		3,905
Accrued capital expenditures	4,832		2,286
Increase (reduction) in capital expenditure accrual	3,663	$ 1,945
Accrued Turnaround Costs	$ 3,330		$ 0