Earnings Per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Earnings Per Share [Abstract]
Net income	$ 15,536	$ 18,814	$ 17,273	$ 17,495	$ 17,036	$ 17,511	$ 17,674	$ 16,211	$ 69,118	$ 68,432	$ 45,925
Less dividends and undistributed earnings allocated to participating securities									(139)	(144)	(108)
Net income available to common shareholders									$ 68,979	$ 68,288	$ 45,817
Weighted average common shares outstanding - basic	17,351,000	17,338,000	17,330,000	17,304,000	17,297,000	17,283,000	17,272,000	17,234,000	17,331,000	17,272,000	17,207,000
Basic earnings per common share (in dollars per share)	$ 0.89	$ 1.08	$ 0.99	$ 1.01	$ 0.98	$ 1.01	$ 1.02	$ 0.94	$ 3.98	$ 3.95	$ 2.66
Less dividends and undistributed earnings allocated to participating securities									$ (139)	$ (144)	$ (108)
Net income available to common shareholders	$ 15,502	$ 18,778	$ 17,238	$ 17,461	$ 17,004	$ 17,475	$ 17,636	$ 16,173	$ 68,979	$ 68,288	$ 45,817
Dilutive effect of common stock equivalents (in shares)									83,000	119,000	131,000
Weighted average common shares outstanding - diluted (in shares)	17,436,000	17,414,000	17,405,000	17,401,000	17,385,000	17,382,000	17,387,000	17,345,000	17,414,000	17,391,000	17,338,000
Diluted earnings per common share (in dollars per share)	$ 0.89	$ 1.08	$ 0.99	$ 1.00	$ 0.98	$ 1.01	$ 1.01	$ 0.93	$ 3.96	$ 3.93	$ 2.64
Antidilutive common stock equivalents									100,643	55,821	11,572