Earnings Per Share (Basic and Diluted Earnings Per Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Earnings Per Share [Abstract]
Net income	$ 76,388	$ 88,132
Weighted-average number of common shares outstanding (for basic calculation)	27,792	27,696
Dilutive stock awards	531	422
Weighted-average number of common shares outstanding (for diluted calculation)	28,323	28,118
Basic earnings per share	$ 2.75	$ 3.18
Diluted earnings per share	$ 2.70	$ 3.13