Earning Per Common Share (Calculation of Earnings Per Share) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Earnings Per Share [Abstract]
Net income	$ 10,935	$ 11,010
Less dividends and undistributed earnings allocated to participating securities	(25)	(39)
Net income applicable to common shareholders	$ 10,910	$ 10,971
Weighted average common shares outstanding - basic	17,023,000	16,759,000
Basic earnings per common share	$ 0.64	$ 0.65
Less dividends and undistributed earnings allocated to participating securities	$ (25)	$ (39)
Net income available to common shareholders	$ 10,910	$ 10,971
Dilutive effect of common stock equivalents	134,000	180,000
Weighted average common shares outstanding - diluted	17,157,000	16,939,000
Diluted earnings per common share	$ 0.64	$ 0.65
Antidilutive common stock equivalents	69,025	77,450