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]
Total equity 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)
Total equity at Mar. 31, 2019	979,947	700,205	(242,572)	473,119	49,195
Total equity at Dec. 31, 2018	934,081	718,271	(242,572)	409,608	48,774
Net income	240,985
Net proceeds from private placement of common units	62,661
Total equity at Sep. 30, 2019	962,731	686,386	(242,572)	470,977	47,940
Total equity at Mar. 31, 2019	979,947	700,205	(242,572)	473,119	49,195
Net income	80,110	66,377		8,222	5,511
Net proceeds from private placement of common units	(18)			(18)
Quarterly distribution to unitholders	(15,666)			(9,379)	(6,287)
Quarterly distribution to noncontrolling interest retained in OpCo by Westlake	(72,259)	(72,259)
Total equity at Jun. 30, 2019	972,114	694,323	(242,572)	471,944	48,419
Net income	82,479	67,557		8,934	5,988
Net proceeds from private placement of common units	(255)			(255)
Quarterly distribution to unitholders	(16,113)			9,646	(6,467)
Quarterly distribution to noncontrolling interest retained in OpCo by Westlake	(75,494)	(75,494)
Total equity at Sep. 30, 2019	962,731	686,386	(242,572)	470,977	47,940
Total equity at Dec. 31, 2019	952,135	674,621	(242,572)	471,736	48,350
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
Net income	265,995
Net proceeds from private placement of common units	0
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
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
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