Earnings Per Share (Details 2) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings Per Share [Abstract]
Distributed earnings allocated to common stock	$ 19,701	$ 18,707	$ 17,582
Undistributed earnings allocated to common stock	47,830	38,670	39,336
Net earnings allocated to common stock	67,531	57,377	56,918
Net earnings allocated to participating securities	520	409	568
Net income available to common shareholders	$ 68,051	$ 57,786	$ 57,486
Weighted average shares outstanding for basic earnings per common share	25,925,820	25,879,397	26,173,351
Dilutive effect of stock compensation (in shares)	0	0	0
Weighted average shares outstanding for diluted earnings per common share	25,925,820	25,879,397	26,173,351
Basic earnings per common share (in dollars per share)	$ 2.60	$ 2.22	$ 2.17
Diluted earnings per common share (in dollars per share)	$ 2.60	$ 2.22	$ 2.17