Related Party Transactions (Debt Payable to Related Parties) (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Related Party Transaction [Line Items]
Interest on related party debt payable	$ 19,623	$ 21,433	$ 21,861
Interest capitalized	0	175	$ 435
Accrued interest on related party debt	4,186	5,448
Long-term debt payable to Westlake	399,674	477,608
Accrued Liabilities [Member] \| Affiliated Entity [Member] \| Westlake [Member]
Related Party Transaction [Line Items]
Accrued interest on related party debt	$ 4,187	$ 5,448

Portion of the carrying amount as of the balance sheet date of obligations due all related parties that is payable after one year or beyond the normal operating cycle if longer.

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Amount of interest capitalized during the period.

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Amount of interest expense incurred on a debt or other obligation to related party.

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Carrying value as of the balance sheet date of [accrued] interest payable on all forms of debt, including trade payables, that has been incurred and is unpaid. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

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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.

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