Supplemental Information (Cash Flow Information) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Related Party Transaction [Line Items]
Increase (decrease) in capital expenditure accrual	$ 232	$ 1,823
Interest Paid, Excluding Capitalized Interest, Operating Activities	20,837	20,551	$ 23,063
Income Taxes Paid	655	711	716
State and Local Jurisdiction [Member]
Related Party Transaction [Line Items]
Income Taxes Paid	362	293	301
Reimbursement to Parent for State Tax [Member] | Westlake [Member] | Affiliated Entity [Member]
Related Party Transaction [Line Items]
Income Taxes Paid	$ 293	$ 418	$ 415