Guarantor Disclosures (Condensed Consolidating Financial Information Statement of Cash Flows) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Condensed Financial Statements, Captions [Line Items]
Net income	$ 210,061	$ 169,443	$ 360,468	$ 327,475
Depreciation and amortization			119,983	95,204
Deferred income taxes			3,088	19,359
Net changes in working capital and other			(48,184)	(9,796)
Net cash provided by operating activities			435,355	432,242
Acquisition of business, net of cash acquired			(15,782)	0
Additions to property, plant and equipment	(108,110)	(106,171)	(203,933)	(216,912)
Proceeds from disposition of assets			0	13
Proceeds from sales and maturities of securities			15,037	342,045
Purchase of securities			0	(117,332)
Settlements of derivative instruments			(1,174)	(290)
Net cash used for investing activities			(174,288)	7,524
Intercompany financing			0	0
Intercompany financing—OpCo			0
Net distributions prior to Westlake Partners initial public offering				0
Dividends paid			(43,896)	(33,623)
Distributions paid			(7,218)
Proceeds from exercise of stock options			831	4,187
Proceeds from issuance of notes payable			2,392	0
Repayment of notes payable			(4,299)	0
Repurchase of common stock for treasury			(62,804)
Windfall tax benefits from share-based payment arrangements			1,895	4,436
Net cash provided by financing activities			(113,099)	(25,000)
Effect of exchange rate changes on cash and cash equivalents			(2,000)	0
Net increase in cash and cash equivalents			145,968	414,766
Cash and cash equivalents at beginning of period			880,601	461,301
Cash and cash equivalents at end of period	1,026,569	876,067	1,026,569	876,067
Westlake Chemical Corporation
Condensed Financial Statements, Captions [Line Items]
Net income	205,095		351,437	327,475
Depreciation and amortization			1,002	730
Deferred income taxes			(40)	(292)
Net changes in working capital and other			(371,716)	(336,669)
Net cash provided by operating activities			(19,317)	(8,756)
Acquisition of business, net of cash acquired			0
Additions to property, plant and equipment			0	0
Proceeds from disposition of assets				0
Proceeds from sales and maturities of securities			15,037	342,045
Purchase of securities				(117,332)
Settlements of derivative instruments			0	0
Net cash used for investing activities			15,037	224,713
Intercompany financing			208,692	221,745
Intercompany financing—OpCo			0
Net distributions prior to Westlake Partners initial public offering				0
Dividends paid			(43,896)	(33,623)
Distributions paid			0
Proceeds from exercise of stock options			831	4,187
Proceeds from issuance of notes payable			0
Repayment of notes payable			0
Repurchase of common stock for treasury			(62,804)
Windfall tax benefits from share-based payment arrangements			1,895	4,436
Net cash provided by financing activities			104,718	196,745
Effect of exchange rate changes on cash and cash equivalents			0
Net increase in cash and cash equivalents			100,438	412,702
Cash and cash equivalents at beginning of period			655,947	420,948
Cash and cash equivalents at end of period	756,385	833,650	756,385	833,650
100% Owned Guarantor Subsidiaries
Condensed Financial Statements, Captions [Line Items]
Net income	167,066		304,242	334,394
Depreciation and amortization			59,792	54,121
Deferred income taxes			929	12,931
Net changes in working capital and other			(310,600)	(336,097)
Net cash provided by operating activities			54,363	65,349
Acquisition of business, net of cash acquired			0
Additions to property, plant and equipment			(95,363)	(110,338)
Proceeds from disposition of assets				12
Proceeds from sales and maturities of securities			0	0
Purchase of securities				0
Settlements of derivative instruments			(1,174)	0
Net cash used for investing activities			(96,537)	(110,326)
Intercompany financing			(269,281)	(329,044)
Intercompany financing—OpCo			135,341
Net distributions prior to Westlake Partners initial public offering				376,613
Dividends paid			0	0
Distributions paid			176,980
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
Windfall tax benefits from share-based payment arrangements			0	0
Net cash provided by financing activities			43,040	47,569
Effect of exchange rate changes on cash and cash equivalents			0
Net increase in cash and cash equivalents			866	2,592
Cash and cash equivalents at beginning of period			3,057	6,227
Cash and cash equivalents at end of period	3,923	8,819	3,923	8,819
OpCo (Less Than 100% Owned Guarantor Subsidiary)
Condensed Financial Statements, Captions [Line Items]
Net income	88,556		177,899	297,718
Depreciation and amortization			40,195	39,282
Deferred income taxes			(234)	6,813
Net changes in working capital and other			15,748	35,108
Net cash provided by operating activities			233,608	378,921
Acquisition of business, net of cash acquired			0
Additions to property, plant and equipment			(95,514)	(106,191)
Proceeds from disposition of assets				0
Proceeds from sales and maturities of securities			0	0
Purchase of securities				0
Settlements of derivative instruments			0	(290)
Net cash used for investing activities			(95,514)	(106,481)
Intercompany financing			53,354	104,173
Intercompany financing—OpCo			(135,341)
Net distributions prior to Westlake Partners initial public offering				(376,613)
Dividends paid			0	0
Distributions paid			(189,103)
Purchase of limited partner interests			135,341
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
Windfall tax benefits from share-based payment arrangements			0	0
Net cash provided by financing activities			(135,749)	(272,440)
Effect of exchange rate changes on cash and cash equivalents			0
Net increase in cash and cash equivalents			2,345	0
Cash and cash equivalents at beginning of period			131,545	0
Cash and cash equivalents at end of period	133,890	0	133,890	0
Non-Guarantor Subsidiaries
Condensed Financial Statements, Captions [Line Items]
Net income	43,788		59,996	(2,102)
Depreciation and amortization			18,994	1,071
Deferred income taxes			2,433	(93)
Net changes in working capital and other			85,278	(2,148)
Net cash provided by operating activities			166,701	(3,272)
Acquisition of business, net of cash acquired			(15,782)
Additions to property, plant and equipment			(13,056)	(383)
Proceeds from disposition of assets				1
Proceeds from sales and maturities of securities			0	0
Purchase of securities				0
Settlements of derivative instruments			0	0
Net cash used for investing activities			2,726	(382)
Intercompany financing			7,235	3,126
Intercompany financing—OpCo			0
Net distributions prior to Westlake Partners initial public offering				0
Dividends paid			0	0
Distributions paid			4,905
Purchase of limited partner interests			(135,341)
Proceeds from exercise of stock options			0	0
Proceeds from issuance of notes payable			2,392
Repayment of notes payable			(4,299)
Repurchase of common stock for treasury			0
Windfall tax benefits from share-based payment arrangements			0	0
Net cash provided by financing activities			(125,108)	3,126
Effect of exchange rate changes on cash and cash equivalents			(2,000)
Net increase in cash and cash equivalents			42,319	(528)
Cash and cash equivalents at beginning of period			90,052	34,126
Cash and cash equivalents at end of period	132,371	33,598	132,371	33,598
Eliminations
Condensed Financial Statements, Captions [Line Items]
Net income	(294,444)		(533,106)	(630,010)
Depreciation and amortization			0	0
Deferred income taxes			0	0
Net changes in working capital and other			533,106	630,010
Net cash provided by operating activities			0	0
Acquisition of business, net of cash acquired			0
Additions to property, plant and equipment			0	0
Proceeds from disposition of assets				0
Proceeds from sales and maturities of securities			0	0
Purchase of securities				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
Dividends paid			0	0
Distributions paid			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
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
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