Earnings Per Common Share (Calculation of Earnings Per Share) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Earnings Per Share [Abstract]
Net income	$ 18,751	$ 18,322	$ 56,682	$ 51,263
Less dividends and undistributed earnings allocated to participating securities	(55)	(37)	(163)	(109)
Net income available to common shareholders	$ 18,696	$ 18,285	$ 56,519	$ 51,154
Weighted average common shares outstanding - basic	17,320,000	17,260,000	17,303,000	17,287,000
Basic earnings per common share	$ 1.08	$ 1.06	$ 3.27	$ 2.96
Less dividends and undistributed earnings allocated to participating securities	$ (54)	$ (37)	$ (162)	$ (109)
Net income available to common shareholders	$ 18,697	$ 18,285	$ 56,520	$ 51,154
Dilutive effect of common stock equivalents	124,000	57,000	148,000	82,000
Weighted average common shares outstanding - diluted	17,444,000	17,317,000	17,451,000	17,369,000
Diluted earnings per common share	$ 1.07	$ 1.06	$ 3.24	$ 2.95
Antidilutive common stock equivalents	148,542	223,210	149,675	221,047