Stockholders' Equity (Changes in Stockholders' Equity) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Schedule of Capitalization, Equity [Line Items]
Amount, beginning balance			$ 3,201,888	$ 2,418,603
Net income	$ 188,420	$ 170,156	548,888	497,631
Pension and other post- retirement benefits liability			1,190	383
Foreign currency translation adjustments			(43,746)	(37,882)
Net unrealized holding gains on investments			124	3,682
Common stock repurchased			(122,249)	(9,495)
Shares issued—stock- based compensation			984	5,502
Stock-based compensation, net of tax on stock options exercised			9,996	13,526
Dividends paid			(67,852)	(55,690)
Distributions to noncontrolling interests			(10,982)
Noncontrolling interest in acquired business			1,597
Issuance of Westlake Chemical Partners LP common units				286,088
Amount, ending balance	3,519,838	3,122,348	3,519,838	3,122,348
Common Stock [Member]
Schedule of Capitalization, Equity [Line Items]
Amount, beginning balance			1,347	1,346
Shares issued—stock- based compensation			0	1
Amount, ending balance	1,347	1,347	1,347	1,347
Treasury Stock [Member]
Schedule of Capitalization, Equity [Line Items]
Amount, beginning balance			(96,372)	(46,220)
Common stock repurchased			(122,249)	(9,495)
Shares issued—stock- based compensation			1,079	2,467
Amount, ending balance	(217,542)	(53,248)	(217,542)	(53,248)
Additional Paid-in Capital [Member]
Schedule of Capitalization, Equity [Line Items]
Amount, beginning balance			530,441	511,432
Shares issued—stock- based compensation			(95)	3,034
Stock-based compensation, net of tax on stock options exercised			9,996	13,526
Amount, ending balance	540,342	527,992	540,342	527,992
Retained Earnings [Member]
Schedule of Capitalization, Equity [Line Items]
Amount, beginning balance			2,555,528	1,954,661
Net income			535,041	495,232
Dividends paid			(67,852)	(55,690)
Amount, ending balance	3,022,717	2,394,203	3,022,717	2,394,203
AOCI Attributable to Parent [Member]
Schedule of Capitalization, Equity [Line Items]
Amount, beginning balance			(79,433)	(2,616)
Pension and other post- retirement benefits liability			1,190	383
Foreign currency translation adjustments			(43,746)	(37,882)
Net unrealized holding gains on investments			124	3,682
Amount, ending balance	(121,865)	(36,433)	(121,865)	(36,433)
Noncontrolling Interest [Member]
Schedule of Capitalization, Equity [Line Items]
Amount, beginning balance			290,377	0
Net income			13,847	2,399
Distributions to noncontrolling interests			(10,982)	0
Noncontrolling interest in acquired business			1,597
Issuance of Westlake Chemical Partners LP common units				286,088
Amount, ending balance	$ 294,839	$ 288,487	$ 294,839	$ 288,487