Long-Term Debt (Schedule of Long-term Debt) (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016
Debt Instrument [Line Items]
Principal Amount	$ 3,602,889	$ 3,677,889
Unamortized Premium, Discount and Debt Issuance Costs,	(1,247)	765
Net, Long-term Debt	3,601,642	3,678,654
Line of Credit [Member] \| Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Principal Amount	250,000	325,000
Unamortized Premium, Discount and Debt Issuance Costs,	0	0
Net, Long-term Debt	$ 250,000	325,000
Senior Notes [Member] \| 4.625% Senior Notes Due 2021 (New Westlake 2021 Notes) [Member]
Debt Instrument [Line Items]
Debt Instrument Maturity	2021
Stated interest rate (percent)	4.625%		4.625%
Principal Amount	$ 624,793	624,793
Unamortized Premium, Discount and Debt Issuance Costs,	25,123	26,837
Net, Long-term Debt	$ 649,916	651,630
Senior Notes [Member] \| 4.625% Senior Notes Due 2021 (Existing Axiall 2021 Notes) [Member]
Debt Instrument [Line Items]
Debt Instrument Maturity	2021
Stated interest rate (percent)	4.625%		4.625%
Principal Amount	$ 63,207	63,207	$ 688,000
Unamortized Premium, Discount and Debt Issuance Costs,	2,690	2,862
Net, Long-term Debt	$ 65,897	66,069
Senior Notes [Member] \| 3.60% Senior Notes Due 2022 [Member]
Debt Instrument [Line Items]
Debt Instrument Maturity	2022
Stated interest rate (percent)	3.60%
Principal Amount	$ 250,000	250,000
Unamortized Premium, Discount and Debt Issuance Costs,	(1,806)	(1,891)
Net, Long-term Debt	$ 248,194	248,109
Senior Notes [Member] \| 4.875% Senior Notes Due 2023 (New Westlake 2023 Notes) [Member]
Debt Instrument [Line Items]
Debt Instrument Maturity	2023
Stated interest rate (percent)	4.875%		4.875%
Principal Amount	$ 433,793	433,793
Unamortized Premium, Discount and Debt Issuance Costs,	12,840	13,431
Net, Long-term Debt	$ 446,633	447,224
Senior Notes [Member] \| 4.875% Senior Notes Due 2023 (Existing Axiall 2023 Notes) [Member]
Debt Instrument [Line Items]
Debt Instrument Maturity	2023
Stated interest rate (percent)	4.875%		4.875%
Principal Amount	$ 16,207	16,207	$ 450,000
Unamortized Premium, Discount and Debt Issuance Costs,	519	540
Net, Long-term Debt	$ 16,726	16,747
Senior Notes [Member] \| 3.6% Senior Notes Due 2026 [Member]
Debt Instrument [Line Items]
Debt Instrument Maturity	2026
Stated interest rate (percent)	3.60%
Principal Amount	$ 750,000	750,000
Unamortized Premium, Discount and Debt Issuance Costs,	(10,564)	(10,757)
Net, Long-term Debt	$ 739,436	739,243
Senior Notes [Member] \| Loan related to tax-exempt waste disposal revenue bonds due 2027 [Member]
Debt Instrument [Line Items]
Debt Instrument Maturity	2027
Principal Amount	$ 10,889	10,889
Unamortized Premium, Discount and Debt Issuance Costs,	0	0
Net, Long-term Debt	$ 10,889	10,889
Senior Notes [Member] \| 6 1/2% Senior Notes Due 2029 [Member]
Debt Instrument [Line Items]
Debt Instrument Maturity	2029
Stated interest rate (percent)	6.50%
Principal Amount	$ 100,000	100,000
Unamortized Premium, Discount and Debt Issuance Costs,	(898)	(916)
Net, Long-term Debt	$ 99,102	99,084
Senior Notes [Member] \| 6 3/4% Senior Notes Due 2032 [Member]
Debt Instrument [Line Items]
Debt Instrument Maturity	2032
Stated interest rate (percent)	6.75%
Principal Amount	$ 250,000	250,000
Unamortized Premium, Discount and Debt Issuance Costs,	(1,853)	(1,883)
Net, Long-term Debt	$ 248,147	248,117
Senior Notes [Member] \| 2035 GO Zone 6 1/2% Notes [Member]
Debt Instrument [Line Items]
Debt Instrument Maturity	2035
Stated interest rate (percent)	6.50%
Principal Amount	$ 89,000	89,000
Unamortized Premium, Discount and Debt Issuance Costs,	(828)	(839)
Net, Long-term Debt	$ 88,172	88,161
Senior Notes [Member] \| 2035 IKE Zone 6 1/2% Notes [Member]
Debt Instrument [Line Items]
Debt Instrument Maturity	2035
Stated interest rate (percent)	6.50%
Principal Amount	$ 65,000	65,000
Unamortized Premium, Discount and Debt Issuance Costs,	(594)	(602)
Net, Long-term Debt	$ 64,406	64,398
Senior Notes [Member] \| 5% Senior Notes Due 2046 [Member]
Debt Instrument [Line Items]
Debt Instrument Maturity	2046
Stated interest rate (percent)	5.00%
Principal Amount	$ 700,000	700,000
Unamortized Premium, Discount and Debt Issuance Costs,	(25,876)	(26,017)
Net, Long-term Debt	$ 674,124	$ 673,983

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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Contractual interest rate for funds borrowed, under the debt agreement.

+ References

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

Amount of unamortized debt discount (premium) and debt issuance costs.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28555-108399

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- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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- Definition

Debt Instrument, Maturity

+ References

No definition available.

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