Earning Per Common Share (Calculation of Earnings Per Share) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Earnings Per Share [Abstract]
Net income	$ 16,211	$ 11,782
Less dividends and undistributed earnings allocated to participating securities	(38)	(27)
Net income applicable to common shareholders	$ 16,173	$ 11,755
Weighted average common shares outstanding - basic	17,234,000	17,186,000
Basic earnings per common share	$ 0.94	$ 0.68
Less dividends and undistributed earnings allocated to participating securities	$ (38)	$ (27)
Net income available to common shareholders	$ 16,173	$ 11,755
Dilutive effect of common stock equivalents	111,000	107,000
Weighted average common shares outstanding - diluted	17,345,000	17,293,000
Diluted earnings per common share	$ 0.93	$ 0.68
Antidilutive common stock equivalents	45,832	0