Related Party Transactions (Accounts Receivable from and Accounts Payable to Related Parties) (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Related Party Transaction [Line Items]
Receivable under the Investment Management Agreement—Westlake Chemical Corporation (Westlake)	$ 171,391		$ 171,391		$ 162,773
Accounts payable—Westlake	5,440		5,440		15,201
Affiliated Entity [Member] \| Westlake [Member]
Related Party Transaction [Line Items]
Interest earned related to the IMA	219	$ 1,155	807	$ 1,973
Accounts receivable—Westlake, current and non-current	$ 42,354		$ 42,354		$ 42,847

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
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
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-Section S99
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section S99
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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant