Earnings per Share (Reconciliation between Basic and Diluted Earnings per Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Earnings Per Share [Abstract]
Net income for basic and diluted earnings per share	$ 29,180	$ 23,434	$ 55,388	$ 49,861
Basic weighted average shares outstanding	31,465	31,490	31,474	31,648
Dilutive effect of stock options and restricted stock awards	161	147	169	157
Diluted weighted average shares outstanding	31,626	31,637	31,643	31,805
Basic earnings per common share	$ 0.93	$ 0.74	$ 1.76	$ 1.58
Diluted earnings per common share	$ 0.92	$ 0.74	$ 1.75	$ 1.57