Earnings Per Common Share Computations (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Earnings Per Share [Abstract]
Net earnings	$ 4,203	$ 3,531	$ 57,689	$ 60,164
Net earnings allocated to participating securities	(67)	(37)	(927)	(623)
Numerator for basic earnings per common share	4,136	3,494	56,762	59,541
Numerator for diluted earnings per common share	$ 4,203	$ 3,531	$ 57,689	$ 60,164
Earnings Per Share, Basic and Diluted [Abstract]
Basic	17,347	17,020	17,316	17,322
Plus dilutive effect of stock options and restricted stock	139	102	116	167
Plus dilutive effect of participating securities	283	181	283	181
Diluted	17,769	17,303	17,715	17,670
Earnings Per Share, Diluted [Abstract]
Basic	$ 0.24	$ 0.21	$ 3.28	$ 3.44
Diluted	$ 0.24	$ 0.20	$ 3.26	$ 3.40