Stockholders' Equity (Reclassifications in AOCI) (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2015		Jun. 30, 2014		Jun. 30, 2015		Jun. 30, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amortization of benefits liability	$ 675		$ 226		$ 1,327		$ 445
Realized gain on available-for-sale investments	22,058		4,601		31,154		7,110
Provision for income taxes	(98,413)		(92,407)		(176,791)		(175,782)
Net income attributable to Westlake Chemical Corporation	205,095		169,443		351,437		327,475
Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net income attributable to Westlake Chemical Corporation	1,992		653		1,565		502
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]	(173)
Amortization of benefits liability	(675)	[1]	(139)	[1]	(1,327)	[1]	(272)
(Loss) income before income taxes	(675)		(226)		(1,327)		(445)
Provision for income taxes	235		86		460		170
Net income attributable to Westlake Chemical Corporation	(440)		(140)		(867)		(275)
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	3,795		1,237		3,795		1,212
Provision for income taxes	(1,363)		(444)		(1,363)		(435)
Net income attributable to Westlake Chemical Corporation	$ 2,432		$ 793		$ 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.