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, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share [Abstract]
Net income for basic and diluted earnings per share	$ 29,242	$ 24,184	$ 84,630	$ 74,045
Basic weighted average shares outstanding	31,492	31,453	31,480	31,582
Dilutive effect of stock options and restricted stock awards	136	169	158	161
Diluted weighted average shares outstanding	31,628	31,622	31,638	31,743
Basic earnings per common share	$ 0.93	$ 0.77	$ 2.69	$ 2.34
Diluted earnings per common share	$ 0.92	$ 0.76	$ 2.67	$ 2.33