Earnings per Share (Reconciliation between Basic and Diluted Earnings per Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Earnings Per Share [Abstract]
Net income for basic and diluted earnings per share	$ 24,184	$ 24,067	$ 74,045	$ 69,218
Basic weighted average shares outstanding	31,453	32,421	31,582	32,716
Dilutive effect of stock options and restricted stock awards	169	284	161	278
Diluted weighted average shares outstanding	31,622	32,705	31,743	32,994
Basic earnings per common share	$ 0.77	$ 0.74	$ 2.34	$ 2.12
Diluted earnings per common share	$ 0.76	$ 0.74	$ 2.33	$ 2.10