Stockholders' Equity (Reclassifications in AOCI) (Details) - USD ($) $ in Thousands	3 Months Ended				9 Months Ended
	Sep. 30, 2015		Sep. 30, 2014		Sep. 30, 2015		Sep. 30, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amortization of benefits liability	$ 692		$ 240		$ 2,019		$ 685
Realized gain on available-for-sale investments	2,636		(2,670)		33,790		4,440
Provision for income taxes	(60,033)		(124,449)		(236,824)		(300,231)
Net income attributable to Westlake Chemical Corporation	183,604		167,757		535,041		495,232
Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net income attributable to Westlake Chemical Corporation	(451)		(148)		1,114		355
Accumulated Defined Benefit Plans Adjustment | Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Prior service costs	0	[1]	(87)	[1]	0	[1]	(261)
Amortization of benefits liability	(692)	[1]	(153)	[1]	(2,019)	[1]	(424)
(Loss) income before income taxes	(692)		(240)		(2,019)		(685)
Provision for income taxes	241		92		701		263
Net income attributable to Westlake Chemical Corporation	(451)		(148)		(1,318)		(422)
Accumulated Net Unrealized Investment Gain (Loss) [Member] | Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Realized gain on available-for-sale investments	0		0		3,795		1,212
Provision for income taxes	0		0		(1,363)		(435)
Net income attributable to Westlake Chemical Corporation	$ 0		$ 0		$ 2,432		$ 777

[1] These accumulated other comprehensive loss components are included in the computation of net periodic benefit cost. For additional information, please read Note 10 (Employee Benefits) to the financial statements included in the 2014 Form 10-K.