Earning Per Common Share (Calculation of Earnings Per Share) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Earnings Per Share [Abstract]
Net income	$ 21,040	$ 17,273	$ 32,941	$ 34,768
Less dividends and undistributed earnings allocated to participating securities	(40)	(35)	(72)	(69)
Net income available to common shareholders	$ 21,000	$ 17,238	$ 32,869	$ 34,699
Weighted average common shares outstanding - basic	17,257,000	17,330,000	17,301,000	17,317,000
Basic earnings per common share	$ 1.22	$ 0.99	$ 1.90	$ 2.00
Less dividends and undistributed earnings allocated to participating securities	$ (40)	$ (35)	$ (72)	$ (69)
Net income available to common shareholders	$ 21,000	$ 17,238	$ 32,869	$ 34,699
Dilutive effect of common stock equivalents	35,000	75,000	76,000	86,000
Weighted average common shares outstanding - diluted	17,292,000	17,405,000	17,377,000	17,403,000
Diluted earnings per common share	$ 1.21	$ 0.99	$ 1.89	$ 1.99
Antidilutive common stock equivalents	256,721	87,950