Earnings Per Share (Basic and Diluted Earnings Per Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share [Abstract]
Net income	$ 38,204	$ 19,610	$ 144,534	$ 132,460
Weighted-average number of common shares outstanding	27,802	28,415	27,844	28,604
Dilutive stock awards	215	24	123	92
Diluted weighted-average number of common shares outstanding	28,017	28,439	27,967	28,696
Basic earnings per share	$ 1.37	$ 0.69	$ 5.19	$ 4.63
Diluted earnings per share	$ 1.36	$ 0.69	$ 5.17	$ 4.62