Related Party Transactions (Cost of Sales from Related Parties) (Details) - Affiliated Entity [Member] - Westlake [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Related Party Transaction [Line Items]
Feedstock purchased from Westlake and included in cost of sales	$ 366,031	$ 556,362	$ 425,255
Other charges from Westlake and included in cost of sales	106,564	114,364	96,813
Related Parties Amount in Cost of Sales	$ 472,595	$ 670,726	$ 522,068