Guarantor Disclosures (Additional Information) (Detail) $ in Thousands	9 Months Ended
	Sep. 30, 2017 USD ($)
Condensed Financial Statements, Captions [Line Items]
Equity Method Investment, Ownership Percentage	100.00%
3.60%, 5.0%, 4.625%, 4.875% Senior Notes [Member]
Condensed Financial Statements, Captions [Line Items]
Minimum debt amount guaranteed by subsidiaries	$ 5,000
3.60% Senior Notes Due 2022 [Member] | Senior Notes [Member]
Condensed Financial Statements, Captions [Line Items]
Debt Instrument Maturity	2022
3.6% Senior Notes Due 2026 [Member] | Senior Notes [Member]
Condensed Financial Statements, Captions [Line Items]
Debt Instrument Maturity	2026
5% Senior Notes Due 2046 [Member] | Senior Notes [Member]
Condensed Financial Statements, Captions [Line Items]
Debt Instrument Maturity	2046
4.625% Senior Notes Due 2021 (New Westlake 2021 Notes) [Member] | Senior Notes [Member]
Condensed Financial Statements, Captions [Line Items]
Debt Instrument Maturity	2021
4.875% Senior Notes Due 2023 (New Westlake 2023 Notes) [Member] | Senior Notes [Member]
Condensed Financial Statements, Captions [Line Items]
Debt Instrument Maturity	2023