Stockholders' Equity (Reclassifications in AOCI) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Realized gain on available-for-sale investments	$ 9,096		$ 2,509
Provision for income taxes	(78,378)		(83,375)
Net income attributable to Westlake Chemical Corporation	146,342		158,032
Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net income attributable to Westlake Chemical Corporation	(427)		(151)
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]
Net loss	(652)	[1]	(132)	[1]
Income before income taxes	(652)		(219)
Provision for income taxes	225		84
Net income attributable to Westlake Chemical Corporation	(427)		(135)
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		(25)
Provision for income taxes	0		9
Net income attributable to Westlake Chemical Corporation	$ 0		$ (16)

[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.