Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Earnings Per Share [Abstract]
Basic	104,033	104,530
Dilutive Effect Of Stock Options Restricted Stock And Equity Settled Awards	442	794
Diluted	104,475	105,324
Net income available to common shareholders	$ 120,796	$ 100,900
Earnings (loss) per share - basic	$ 1.16	$ 0.97
Earnings (loss) per share - diluted	$ 1.16	$ 0.96
Anti-dilutive stock options outstanding that were not included in computation of diluted earnings per common share	0