Related Party Transactions (Cost of Sales from Related Parties) (Details) - Affiliated Entity [Member] - Westlake [Member] - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Related Party Transaction [Line Items]
Charges from related parties in cost of sales	$ 149,727	$ 133,821
Feedstock purchased [Member]
Related Party Transaction [Line Items]
Charges from related parties in cost of sales	122,155	105,415
Other service charges [Member]
Related Party Transaction [Line Items]
Charges from related parties in cost of sales	$ 27,572	$ 28,406

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=115205541&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

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