Stockholders' Equity (Changes in Stockholders Equity) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			$ 3,892,045	$ 3,561,931
Net income	$ 219,150	$ 70,014	523,278	314,570
Pension and other post- retirement benefits liability			1,013	409
Foreign currency translation adjustments			109,515	15,758
Other			(260)	4,999
Common stock repurchased				(66,725)
Shares issued—stock- based compensation			2,204	1,650
Stock-based compensation, net of tax on stock options exercised			10,223	7,778
Dividends declared			(76,491)	(71,933)
Distributions to noncontrolling interests			(20,767)	(12,300)
Issuance of Westlake Chemical Partners LP common units			110,739
Noncontrolling interest in acquired business				68,000
Ending balance	4,551,499	3,824,137	4,551,499	3,824,137
Common Stock [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			1,347	1,347
Shares issued—stock- based compensation			0	0
Ending balance	1,347	1,347	1,347	1,347
Common Stock, Held in Treasury [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			(319,339)	(258,312)
Common stock repurchased				(66,725)
Shares issued—stock- based compensation			4,645	5,057
Ending balance	(314,694)	(319,980)	(314,694)	(319,980)
Additional Paid-in Capital [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			550,641	542,148
Shares issued—stock- based compensation			(2,441)	(3,407)
Stock-based compensation, net of tax on stock options exercised			10,223	7,778
Ending balance	558,423	546,519	558,423	546,519
Retained Earnings [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			3,412,286	3,109,987
Net income			501,849	299,914
Dividends declared			(76,491)	(71,933)
Ending balance	3,837,644	3,337,968	3,837,644	3,337,968
Accumulated Other Comprehensive Income (Loss) [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			(121,306)	(129,292)
Pension and other post- retirement benefits liability			1,057	409
Foreign currency translation adjustments			106,563	15,758
Other			(260)	4,999
Ending balance	(13,946)	(108,126)	(13,946)	(108,126)
Noncontrolling Interest [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			368,416	296,053
Net income			21,429	14,656
Pension and other post- retirement benefits liability			(44)
Foreign currency translation adjustments			2,952
Distributions to noncontrolling interests			(20,767)	(12,300)
Issuance of Westlake Chemical Partners LP common units			110,739
Noncontrolling interest in acquired business				68,000
Ending balance	$ 482,725	$ 366,409	$ 482,725	$ 366,409