Segment Information (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2025 USD ($) segment	Mar. 31, 2024 USD ($)	Dec. 31, 2024 USD ($)
Segment Reporting Information [Line Items]
Number of operating segments | segment	1
Depreciation and amortization	$ 27,068	$ 27,994
Cost of sales	183,548	182,493
Selling, general and administrative expenses	7,474	7,077
Interest expense—Westlake	5,537	6,581
Net income	42,309	89,646
Assets	1,371,352		$ 1,287,956
Operating Segments | OpCo
Segment Reporting Information [Line Items]
Raw material, energy, manufacturing and logistics costs	156,480	154,499
Depreciation and amortization	27,068	27,994
Cost of sales	183,548	182,493
Selling, general and administrative expenses	6,672	6,052
Other segment items	(971)	(750)
Interest expense—Westlake	268	374
Net income	48,380	96,878
Assets	1,329,150		1,238,420
Corporate
Segment Reporting Information [Line Items]
Interest expense—Westlake	5,269	6,207
Net income	(6,071)	$ (7,232)
Assets	$ 42,202		$ 49,536