Long-Term Debt (Schedule of Long-term Debt) (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Mar. 27, 2017	Dec. 31, 2016	Sep. 30, 2016
Debt Instrument [Line Items]
Principal Amount	$ 3,352,889		$ 3,677,889
Unamortized Premium, Discount and Debt Issuance Costs,	(3,487)		765
Net, Long-term Debt	3,349,402		3,678,654
Line of Credit [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Principal Amount	0		325,000
Unamortized Premium, Discount and Debt Issuance Costs,	0		0
Net, Long-term Debt	$ 0		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	$ 624,793
Unamortized Premium, Discount and Debt Issuance Costs,	21,881		26,837
Net, Long-term Debt	$ 646,674		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%		4.625%
Principal Amount	$ 63,207	$ 63,207	63,207	$ 688,000
Unamortized Premium, Discount and Debt Issuance Costs,	2,343		2,862
Net, Long-term Debt	$ 65,550		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,	(1,635)		(1,891)
Net, Long-term Debt	$ 248,365		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	$ 433,793
Unamortized Premium, Discount and Debt Issuance Costs,	11,791		13,431
Net, Long-term Debt	$ 445,584		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%		4.875%
Principal Amount	$ 16,207	$ 16,207	16,207	$ 450,000
Unamortized Premium, Discount and Debt Issuance Costs,	477		540
Net, Long-term Debt	$ 16,684		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,	(10,031)		(10,757)
Net, Long-term Debt	$ 739,969		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,	(861)		(916)
Net, Long-term Debt	$ 99,139		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,	(605)		(1,883)
Net, Long-term Debt	$ 249,395		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,	(806)		(839)
Net, Long-term Debt	$ 88,194		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,	(578)		(602)
Net, Long-term Debt	$ 64,422		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,	(25,463)		(26,017)
Net, Long-term Debt	$ 674,537		$ 673,983