Earnings and Dividends per Share (Reconciliation of Denominator for Basic and Diluted Earnings Per Share) (Details) - $ / shares	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Earnings and Dividends Per Share [Abstract]
Weighted average common shares—basic	128,237,364	128,528,480
Weighted Average Number Diluted Shares Outstanding Adjustment	205,608	385,441
Weighted average common shares-diluted	128,442,972	128,913,921
Earnings per share attributable to Westlake Chemical Corporation: Basic (in dollars per share)	$ 1.13	$ 0.56
Earnings per share attributable to Westlake Chemical Corporation: Diluted (in dollars per share)	$ 1.13	$ 0.55