Guarantor Disclosures (Condensed Consolidating Financial Information Statement of Cash Flows) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Condensed Financial Statements, Captions [Line Items]
Net income	$ 188,420	$ 170,156	$ 548,888	$ 497,631
Depreciation and amortization			181,733	149,566
Deferred income taxes			7,585	34,459
Net changes in working capital and other			103,094	94,468
Net cash provided by operating activities			841,300	776,124
Acquisition of business, net of cash acquired			15,782	(611,087)
Acquisition of business				(611,087)
Additions to property, plant and equipment	(125,304)	(94,271)	(329,236)	(311,183)
Proceeds from disposition of assets			17	145
Proceeds from repayment of loan acquired			0	45,923
Proceeds from disposition of equity method investment			27,865	0
Proceeds from sales and maturities of securities			16,056	342,045
Purchase of securities			(282,542)	(117,332)
Settlements of derivative instruments			(1,535)	(689)
Net cash used for investing activities			(553,593)	(652,178)
Intercompany financing			0	0
Intercompany financing—OpCo			0
Net distributions prior to Westlake Partners initial public offering				0
Capitalized debt issuance costs			0	(1,167)
Dividends paid			(67,852)	(55,690)
Distributions paid			(10,982)
Net proceeds from issuance of Westlake Partners common units			0	286,088
Purchase of limited partner interests				0
Proceeds from exercise of stock options			984	5,502
Proceeds from issuance of notes payable			19,483	0
Repayment of notes payable			(32,954)	0
Repurchase of common stock for treasury			(114,254)	(9,495)
Windfall tax benefits from share-based payment arrangements			2,452	6,670
Net cash provided by financing activities			(203,123)	231,908
Effect of exchange rate changes on cash and cash equivalents			(3,260)	(3,687)
Net increase in cash and cash equivalents			81,324	352,167
Cash and cash equivalents at beginning of period			880,601	461,301
Cash and cash equivalents at end of period	961,925	813,468	961,925	813,468
Westlake Chemical Corporation
Condensed Financial Statements, Captions [Line Items]
Net income	183,604	167,757	535,041	495,232
Depreciation and amortization			1,504	1,172
Deferred income taxes			87	(418)
Net changes in working capital and other			(567,137)	(509,862)
Net cash provided by operating activities			(30,505)	(13,876)
Acquisition of business, net of cash acquired			0
Acquisition of business				0
Additions to property, plant and equipment			0	0
Proceeds from disposition of assets			0	0
Proceeds from repayment of loan acquired				0
Proceeds from disposition of equity method investment			0
Proceeds from sales and maturities of securities			16,056	342,045
Purchase of securities			(282,542)	(117,332)
Settlements of derivative instruments			0	0
Net cash used for investing activities			(266,486)	224,713
Intercompany financing			467,360	75,104
Intercompany financing—OpCo			0
Net distributions prior to Westlake Partners initial public offering				0
Capitalized debt issuance costs				(1,167)
Dividends paid			(67,852)	(55,690)
Distributions paid			0
Net proceeds from issuance of Westlake Partners common units				0
Purchase of limited partner interests				0
Proceeds from exercise of stock options			984	5,502
Proceeds from issuance of notes payable			0
Repayment of notes payable			0
Repurchase of common stock for treasury			(114,254)	(9,495)
Windfall tax benefits from share-based payment arrangements			2,452	6,670
Net cash provided by financing activities			288,690	20,924
Effect of exchange rate changes on cash and cash equivalents			0	0
Net increase in cash and cash equivalents			(8,301)	231,761
Cash and cash equivalents at beginning of period			655,947	420,948
Cash and cash equivalents at end of period	647,646	652,709	647,646	652,709
100% Owned Guarantor Subsidiaries
Condensed Financial Statements, Captions [Line Items]
Net income	169,422	175,009	473,663	509,404
Depreciation and amortization			90,247	82,597
Deferred income taxes			4,184	26,991
Net changes in working capital and other			(251,423)	(919,521)
Net cash provided by operating activities			316,671	(300,529)
Acquisition of business, net of cash acquired			0
Acquisition of business				0
Additions to property, plant and equipment			(148,055)	(160,147)
Proceeds from disposition of assets			0	144
Proceeds from repayment of loan acquired				0
Proceeds from disposition of equity method investment			27,865
Proceeds from sales and maturities of securities			0	0
Purchase of securities			0	0
Settlements of derivative instruments			(1,535)	(556)
Net cash used for investing activities			(121,725)	(160,559)
Intercompany financing			(577,898)	(143,325)
Intercompany financing—OpCo			135,341
Net distributions prior to Westlake Partners initial public offering				448,101
Capitalized debt issuance costs				0
Dividends paid			0	151,729
Distributions paid			249,999
Net proceeds from issuance of Westlake Partners common units				0
Purchase of limited partner interests				0
Proceeds from exercise of stock options			0	0
Proceeds from issuance of notes payable			0
Repayment of notes payable			0
Repurchase of common stock for treasury			0	0
Windfall tax benefits from share-based payment arrangements			0	0
Net cash provided by financing activities			(192,558)	456,505
Effect of exchange rate changes on cash and cash equivalents			0	0
Net increase in cash and cash equivalents			2,388	(4,583)
Cash and cash equivalents at beginning of period			3,057	6,227
Cash and cash equivalents at end of period	5,445	1,644	5,445	1,644
OpCo (Less Than 100% Owned Guarantor Subsidiary)
Condensed Financial Statements, Captions [Line Items]
Net income	88,722	119,019	266,621	416,737
Depreciation and amortization			60,637	58,501
Deferred income taxes			(359)	8,267
Net changes in working capital and other			9,315	1,641
Net cash provided by operating activities			336,214	485,146
Acquisition of business, net of cash acquired			0
Acquisition of business				0
Additions to property, plant and equipment			(152,572)	(144,348)
Proceeds from disposition of assets			0	0
Proceeds from repayment of loan acquired				0
Proceeds from disposition of equity method investment			0
Proceeds from sales and maturities of securities			0	0
Purchase of securities			0	0
Settlements of derivative instruments			0	(133)
Net cash used for investing activities			(152,572)	(144,481)
Intercompany financing			102,857	62,221
Intercompany financing—OpCo			(135,341)
Net distributions prior to Westlake Partners initial public offering				(448,101)
Capitalized debt issuance costs				0
Dividends paid			0	(151,729)
Distributions paid			(268,562)
Net proceeds from issuance of Westlake Partners common units				0
Purchase of limited partner interests			135,341	286,088
Proceeds from exercise of stock options			0	0
Proceeds from issuance of notes payable			0
Repayment of notes payable			0
Repurchase of common stock for treasury			0	0
Windfall tax benefits from share-based payment arrangements			0	0
Net cash provided by financing activities			(165,705)	(251,521)
Effect of exchange rate changes on cash and cash equivalents			0	0
Net increase in cash and cash equivalents			17,937	89,144
Cash and cash equivalents at beginning of period			131,545	0
Cash and cash equivalents at end of period	149,482	89,144	149,482	89,144
Non-Guarantor Subsidiaries
Condensed Financial Statements, Captions [Line Items]
Net income	25,719	663	85,715	(1,441)
Depreciation and amortization			29,345	7,296
Deferred income taxes			3,673	(381)
Net changes in working capital and other			100,187	599,909
Net cash provided by operating activities			218,920	605,383
Acquisition of business, net of cash acquired			15,782
Acquisition of business				(611,087)
Additions to property, plant and equipment			(28,609)	(6,688)
Proceeds from disposition of assets			17	1
Proceeds from repayment of loan acquired				45,923
Proceeds from disposition of equity method investment			0
Proceeds from sales and maturities of securities			0	0
Purchase of securities			0	0
Settlements of derivative instruments			0	0
Net cash used for investing activities			(12,810)	(571,851)
Intercompany financing			7,681	6,000
Intercompany financing—OpCo			0
Net distributions prior to Westlake Partners initial public offering				0
Capitalized debt issuance costs				0
Dividends paid			0	0
Distributions paid			7,581
Net proceeds from issuance of Westlake Partners common units				286,088
Purchase of limited partner interests			(135,341)	(286,088)
Proceeds from exercise of stock options			0	0
Proceeds from issuance of notes payable			19,483
Repayment of notes payable			(32,954)
Repurchase of common stock for treasury			0	0
Windfall tax benefits from share-based payment arrangements			0	0
Net cash provided by financing activities			(133,550)	6,000
Effect of exchange rate changes on cash and cash equivalents			(3,260)	(3,687)
Net increase in cash and cash equivalents			69,300	35,845
Cash and cash equivalents at beginning of period			90,052	34,126
Cash and cash equivalents at end of period	159,352	69,971	159,352	69,971
Eliminations
Condensed Financial Statements, Captions [Line Items]
Net income	(279,047)	(292,292)	(812,152)	(922,301)
Depreciation and amortization			0	0
Deferred income taxes			0	0
Net changes in working capital and other			812,152	922,301
Net cash provided by operating activities			0	0
Acquisition of business, net of cash acquired			0
Acquisition of business				0
Additions to property, plant and equipment			0	0
Proceeds from disposition of assets			0	0
Proceeds from repayment of loan acquired				0
Proceeds from disposition of equity method investment			0
Proceeds from sales and maturities of securities			0	0
Purchase of securities			0	0
Settlements of derivative instruments			0	0
Net cash used for investing activities			0	0
Intercompany financing			0	0
Intercompany financing—OpCo			0
Net distributions prior to Westlake Partners initial public offering				0
Capitalized debt issuance costs				0
Dividends paid			0	0
Distributions paid			0
Net proceeds from issuance of Westlake Partners common units				0
Purchase of limited partner interests				0
Proceeds from exercise of stock options			0	0
Proceeds from issuance of notes payable			0
Repayment of notes payable			0
Repurchase of common stock for treasury			0	0
Windfall tax benefits from share-based payment arrangements			0	0
Net cash provided by financing activities			0	0
Effect of exchange rate changes on cash and cash equivalents			0	0
Net increase in cash and cash equivalents			0	0
Cash and cash equivalents at beginning of period			0	0
Cash and cash equivalents at end of period	$ 0	$ 0	$ 0	$ 0