Earnings and Dividends per Share (Reconciliation of Denominator for Basic and Diluted Earnings Per Share) (Details) - $ / shares	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share [Abstract]
Weighted average common shares—basic	129,427,328	129,069,186	129,512,097	129,033,597
Incremental Shares From Assumed exercise of options	624,964	819,782	671,104	756,368
Weighted average common shares-diluted	130,052,292	129,888,968	130,183,201	129,789,965
Earnings per share attributable to Westlake Chemical Corporation: Basic	$ 2.36	$ 1.62	$ 6.70	$ 3.87
Earnings per share attributable to Westlake Chemical Corporation: Diluted	$ 2.35	$ 1.61	$ 6.67	$ 3.85