Earning Per Common Share (Calculation of Earnings Per Share) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Earnings Per Share [Abstract]
Net income	$ 18,814	$ 17,511	$ 53,582	$ 51,396
Less dividends and undistributed earnings allocated to participating securities	(36)	(36)	(105)	(112)
Net income applicable to common shareholders	$ 18,778	$ 17,475	$ 53,477	$ 51,284
Weighted average common shares outstanding - basic	17,338,000	17,283,000	17,324,000	17,263,000
Basic earnings per common share	$ 1.08	$ 1.01	$ 3.09	$ 2.97
Less dividends and undistributed earnings allocated to participating securities	$ (36)	$ (36)	$ (105)	$ (112)
Net income applicable to common shareholders	$ 18,778	$ 17,475	$ 53,477	$ 51,284
Dilutive effect of common stock equivalents	76,000	99,000	82,000	129,000
Weighted average common shares outstanding - diluted	17,414,000	17,382,000	17,406,000	17,392,000
Diluted earnings per common share	$ 1.08	$ 1.01	$ 3.07	$ 2.95
Antidilutive common stock equivalents	93,075	41,525	87,775	46,692