Earning Per Common Share (Calculation of Earnings Per Share) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Earnings Per Share [Abstract]
Net income	$ 17,495	$ 16,211
Less dividends and undistributed earnings allocated to participating securities	(34)	(38)
Net income applicable to common shareholders	$ 17,461	$ 16,173
Weighted average common shares outstanding - basic	17,304,000	17,234,000
Basic earnings per common share	$ 1.01	$ 0.94
Less dividends and undistributed earnings allocated to participating securities	$ (34)	$ (38)
Net income applicable to common shareholders	$ 17,461	$ 16,173
Dilutive effect of common stock equivalents	97,000	111,000
Weighted average common shares outstanding - diluted	17,401,000	17,345,000
Diluted earnings per common share	$ 1.00	$ 0.93
Antidilutive common stock equivalents	87,775	45,832