Related Party Transactions (Cost of Sales from Related Parties) (Details) - Affiliated Entity [Member] - Westlake [Member] - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Related Party Transaction [Line Items]
Charges from related parties in cost of sales	$ 83,812	$ 99,803	$ 260,772	$ 366,593
Feedstock Purchased [Member]
Related Party Transaction [Line Items]
Charges from related parties in cost of sales	60,646	73,813	189,608	285,567
Other service charges [Member]
Related Party Transaction [Line Items]
Charges from related parties in cost of sales	$ 23,166	$ 25,990	$ 71,164	$ 81,026

Amount included in cost of sales related to transactions with related parties incurred and recorded in the statement of operations for the period.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03(2))
-URI http://asc.fasb.org/extlink&oid=120395209&loc=SL114868664-224227

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=84158767&loc=d3e18780-107790

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration