Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash flows from operating activities
Net income	$ 332,895	$ 330,571	$ 353,058
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	107,320	108,842	113,985
Loss from disposition of property, plant and equipment	515	1,849	3,033
Other gains, net	(459)	(347)	(1,040)
Changes in operating assets and liabilities
Accounts receivable - third parties	6,934	1,470	(6,146)
Net accounts receivable - Westlake	2,358	(442)	84,652
Inventories	1,126	1,202	(1,656)
Prepaid expenses and other current assets	(100)	(56)	(45)
Accounts payable	421	(4,476)	1,442
Accrued and other liabilities	985	(1,974)	(9)
Other, net	(1,188)	(488)	(9,917)
Net cash provided by operating activities	450,807	436,151	537,357
Cash flows from investing activities
Additions to property, plant and equipment	(43,707)	(39,862)	(68,858)
Maturities of investments with Westlake under the Investment Management Agreement	515,445	372,050	62,828
Investments with Westlake under the Investment Management Agreement	(529,445)	(384,000)	(199,000)
Other	0	0	1,801
Net cash used for investing activities	(57,707)	(51,812)	(203,229)
Cash flows from financing activities
Net proceeds from private placement of common units	62,661	0	110,698
Proceeds from debt payable to Westlake	123,511	3,648	165,257
Repayment of debt payable to Westlake	(201,445)	0	(285,926)
Quarterly distributions to noncontrolling interest retained in OpCo by Westlake	(315,564)	(341,888)	(343,932)
Quarterly distributions to unitholders	(62,084)	(53,363)	(42,117)
Net cash used for financing activities	(392,921)	(391,603)	(396,020)
Net increase (decrease) in cash and cash equivalents	179	(7,264)	(61,892)
Cash and cash equivalents at beginning of the year	19,744	27,008	88,900
Cash and cash equivalents at end of the year	$ 19,923	$ 19,744	$ 27,008