Guarantor Disclosures (Condensed Consolidating Financial Information Balance Sheets) (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014	Dec. 31, 2013
Condensed Financial Statements, Captions [Line Items]
Cash and cash equivalents	$ 961,925	$ 880,601	$ 813,468	$ 461,301
Marketable securities	285,726	0
Accounts receivable, net	520,960	560,666
Inventories	430,006	525,776
Prepaid expenses and other current assets	18,272	11,807
Deferred income taxes	31,541	32,437
Total current assets	2,248,430	2,011,287
Property, plant and equipment, net	2,916,630	2,757,557
Equity investments	9,593	61,305
Other assets, net	349,752	383,841
Total assets	5,524,405	5,213,990
Accounts payable		261,062
Accounts and notes payable	244,772	261,062
Accrued liabilities	290,115	276,118
Total current liabilities	534,887	537,180
Long-term debt	764,086	763,997
Deferred income taxes	534,824	536,066
Other liabilities	170,770	174,859
Total liabilities	2,004,567	2,012,102
Total Westlake Chemical Corporation stockholders' equity	3,224,999	2,911,511
Noncontrolling interests	294,839	290,377
Total equity	3,519,838	3,201,888	3,122,348	2,418,603
Total liabilities and equity	5,524,405	5,213,990
Westlake Chemical Corporation
Condensed Financial Statements, Captions [Line Items]
Cash and cash equivalents	647,646	655,947	652,709	420,948
Marketable securities	285,726
Accounts receivable, net	9,371	8,451
Inventories	0	0
Prepaid expenses and other current assets	1,355	172
Deferred income taxes	441	409
Total current assets	944,539	664,979
Property, plant and equipment, net	0	0
Equity investments	4,879,268	4,033,378
Other assets, net	17,541	30,543
Total assets	5,841,348	4,728,900
Accounts payable		1,055,527
Accounts and notes payable	1,847,047
Accrued liabilities	16,105	8,754
Total current liabilities	1,863,152	1,064,281
Long-term debt	753,197	753,108
Deferred income taxes	0	0
Other liabilities	0	0
Total liabilities	2,616,349	1,817,389
Total Westlake Chemical Corporation stockholders' equity	3,224,999	2,911,511
Noncontrolling interests	0	0
Total equity	3,224,999	2,911,511
Total liabilities and equity	5,841,348	4,728,900
100% Owned Guarantor Subsidiaries
Condensed Financial Statements, Captions [Line Items]
Cash and cash equivalents	5,445	3,057	1,644	6,227
Marketable securities	0
Accounts receivable, net	2,165,248	1,454,709
Inventories	333,553	414,975
Prepaid expenses and other current assets	15,244	9,485
Deferred income taxes	30,529	29,832
Total current assets	2,550,019	1,912,058
Property, plant and equipment, net	1,533,456	1,477,515
Equity investments	1,204,734	1,237,080
Other assets, net	353,506	387,325
Total assets	5,641,715	5,013,978
Accounts payable		160,834
Accounts and notes payable	131,438
Accrued liabilities	168,569	203,608
Total current liabilities	300,007	364,442
Long-term debt	10,889	10,889
Deferred income taxes	503,102	497,919
Other liabilities	49,174	43,452
Total liabilities	863,172	916,702
Total Westlake Chemical Corporation stockholders' equity	4,778,543	4,097,276
Noncontrolling interests	0	0
Total equity	4,778,543	4,097,276
Total liabilities and equity	5,641,715	5,013,978
OpCo (Less Than 100% Owned Guarantor Subsidiary)
Condensed Financial Statements, Captions [Line Items]
Cash and cash equivalents	149,482	131,545	89,144	0
Marketable securities	0
Accounts receivable, net	58,514	56,049
Inventories	3,272	6,634
Prepaid expenses and other current assets	382	212
Deferred income taxes	0	0
Total current assets	211,650	194,440
Property, plant and equipment, net	962,221	842,057
Equity investments	0	0
Other assets, net	46,542	57,733
Total assets	1,220,413	1,094,230
Accounts payable		17,680
Accounts and notes payable	33,476
Accrued liabilities	21,055	11,225
Total current liabilities	54,531	28,905
Long-term debt	195,154	227,638
Deferred income taxes	1,489	1,848
Other liabilities	0	0
Total liabilities	251,174	258,391
Total Westlake Chemical Corporation stockholders' equity	969,239	835,839
Noncontrolling interests	0	0
Total equity	969,239	835,839
Total liabilities and equity	1,220,413	1,094,230
Non-Guarantor Subsidiaries
Condensed Financial Statements, Captions [Line Items]
Cash and cash equivalents	159,352	90,052	69,971	34,126
Marketable securities	0
Accounts receivable, net	135,837	135,133
Inventories	93,181	104,167
Prepaid expenses and other current assets	3,576	1,938
Deferred income taxes	647	2,196
Total current assets	392,593	333,486
Property, plant and equipment, net	420,953	437,985
Equity investments	468,760	352,550
Other assets, net	133,196	141,948
Total assets	1,415,502	1,265,969
Accounts payable		95,856
Accounts and notes payable	80,685
Accrued liabilities	86,883	77,372
Total current liabilities	167,568	173,228
Long-term debt	0	0
Deferred income taxes	36,112	42,369
Other liabilities	121,596	131,407
Total liabilities	325,276	347,004
Total Westlake Chemical Corporation stockholders' equity	795,387	628,588
Noncontrolling interests	294,839	290,377
Total equity	1,090,226	918,965
Total liabilities and equity	1,415,502	1,265,969
Eliminations
Condensed Financial Statements, Captions [Line Items]
Cash and cash equivalents	0	0	$ 0	$ 0
Marketable securities	0
Accounts receivable, net	(1,848,010)	(1,093,676)
Inventories	0	0
Prepaid expenses and other current assets	(2,285)	0
Deferred income taxes	(76)	0
Total current assets	(1,850,371)	(1,093,676)
Property, plant and equipment, net	0	0
Equity investments	(6,543,169)	(5,561,703)
Other assets, net	(201,033)	(233,708)
Total assets	(8,594,573)	(6,889,087)
Accounts payable		(1,068,835)
Accounts and notes payable	(1,847,874)
Accrued liabilities	(2,497)	(24,841)
Total current liabilities	(1,850,371)	(1,093,676)
Long-term debt	(195,154)	(227,638)
Deferred income taxes	(5,879)	(6,070)
Other liabilities	0	0
Total liabilities	(2,051,404)	(1,327,384)
Total Westlake Chemical Corporation stockholders' equity	(6,543,169)	(5,561,703)
Noncontrolling interests	0	0
Total equity	(6,543,169)	(5,561,703)
Total liabilities and equity	$ (8,594,573)	$ (6,889,087)