Consolidated Statements of Changes in Equity - USD ($) $ in Thousands	Total	Accumulated Other Comprehensive Income (Loss) [Member]	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, 2017	$ 998,749	$ 279	$ 778,935	$ (241,958)	$ 411,228	$ 50,265
Net income	80,714	0	68,419	733	6,498	5,064
Net effect of cash flow hedge	19	19	0	0	0	0
Units issued for vested phantom units	60	0	0	0	60	0
Proceeds from private placement of common units	0
Quarterly distributions to unitholders	(13,071)	0	0	(614)	(7,000)	(5,457)
Quarterly distribution to noncontrolling interest retained in OpCo by Westlake	(91,148)	0	(91,148)	0	0	0
Equity, ending balance at Mar. 31, 2018	975,323	298	756,206	(241,839)	410,786	49,872
Equity, beginning balance at Dec. 31, 2018	934,081	0	718,271	(242,572)	409,608	48,774
Net income	78,396	0	63,441	0	8,422	6,533
Proceeds from private placement of common units	62,934	0	0	0	62,934	0
Quarterly distributions to unitholders	(13,957)	0	0	0	(7,845)	(6,112)
Quarterly distribution to noncontrolling interest retained in OpCo by Westlake	(81,507)	0	(81,507)	0	0	0
Equity, ending balance at Mar. 31, 2019	$ 979,947	$ 0	$ 700,205	$ (242,572)	$ 473,119	$ 49,195