Related Party Transactions (Accounts Receivable from and Accounts Payable to Related Parties) (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Related Party Transaction [Line Items]
Receivable under the Investment Management Agreement—Westlake Chemical Corporation (Westlake)	$ 276,501	$ 148,956
Accounts payable—Westlake	19,344	27,477
Affiliated Entity [Member] \| Westlake [Member]
Related Party Transaction [Line Items]
Accounts receivable—Westlake, current and non-current	$ 47,626	$ 57,280

Amount for accounts payable to related parties. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant