Earning Per Common Share (Calculation of Earnings Per Share) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share [Abstract]
Net income	$ 17,511	$ 12,962	$ 51,396	$ 37,943
Less dividends and undistributed earnings allocated to participating securities	(36)	(28)	(112)	(84)
Net income applicable to common shareholders	$ 17,475	$ 12,934	$ 51,284	$ 37,859
Weighted average common shares outstanding - basic	17,283,000	17,212,000	17,263,000	17,201,000
Basic earnings per common share	$ 1.01	$ 0.75	$ 2.97	$ 2.20
Less dividends and undistributed earnings allocated to participating securities	$ (36)	$ (28)	$ (112)	$ (84)
Net income applicable to common shareholders	$ 17,475	$ 12,934	$ 51,284	$ 37,859
Dilutive effect of common stock equivalents	99,000	106,000	129,000	119,000
Weighted average common shares outstanding - diluted	17,382,000	17,318,000	17,392,000	17,320,000
Diluted earnings per common share	$ 1.01	$ 0.75	$ 2.95	$ 2.19
Antidilutive common stock equivalents	41,525		46,692	0