Description of Business and Significant Accounting Policies (Narrative) (Details) $ / shares in Units, $ in Thousands					12 Months Ended
	Mar. 29, 2019 USD ($) $ / shares shares	Sep. 29, 2017 USD ($) $ / shares shares	Apr. 29, 2015 USD ($)	Aug. 04, 2014 shares	Dec. 31, 2019 USD ($) production_facility	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Proceeds from secondary public offering, net of finance and other offering costs	$ 62,661				$ 62,661	$ 0	$ 110,698
Threshold period past due accounts receivable reviewed					90 days
Capitalized interest					$ 0	175	$ 435
Goodwill					$ 5,814	$ 5,814
Amortization period, minimum (in years)					3 years
Amortization period, maximum (in years)					6 years
Affiliated Entity [Member] | Westlake Chemical OpCo LP [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Partnership's ownership interest (percent)	22.80%			10.60%
Additional ownership interest acquired	4.50%		2.70%
Amount paid to purchase additional limited partner interest	$ 201,445		$ 135,341
Limited Liability Company [Member] | Westlake Chemical OpCo GP LLC [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Partnership's ownership interest (percent)				100.00%
Westlake [Member] | Majority-Owned Subsidiary, Unconsolidated [Member] | Westlake Chemical OpCo LP [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Partnership's ownership interest (percent)	77.20%	18.30%
Westlake Chemical OpCo LP [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Number of Production Facilities | production_facility					3
Limited Partner [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Number of units sold in public offering | shares	2,940,818	5,175,000		12,937,500
Partners' Capital Account, Units, Sold in Public Offering, Price per Unit | $ / shares	$ 21.40	$ 22.00
Proceeds from secondary public offering, net of finance and other offering costs		$ 110,739