Earnings Per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Earnings Per Share [Abstract]
Net income	$ 12,162	$ 12,327	$ 11,057	$ 10,935	$ 10,744	$ 10,208	$ 11,503	$ 11,010	$ 46,481	$ 43,465	$ 40,824
Less dividends and undistributed earnings allocated to participating securities									(97)	(126)	(152)
Net income applicable to common shareholders									$ 46,384	$ 43,339	$ 40,672
Weighted average common shares outstanding - basic	17,142,000	17,090,000	17,067,000	17,023,000	17,004,000	16,939,000	16,811,000	16,759,000	17,081,000	16,879,000	16,689,000
Basic earnings per common share (in dollars per share)	$ 0.71	$ 0.72	$ 0.65	$ 0.64	$ 0.63	$ 0.60	$ 0.68	$ 0.65	$ 2.72	$ 2.57	$ 2.44
Less dividends and undistributed earnings allocated to participating securities									$ (97)	$ (126)	$ (151)
Net income applicable to common shareholders									$ 46,384	$ 43,339	$ 40,673
Dilutive effect of common stock equivalents (in shares)									127,000	188,000	183,000
Weighted average common shares outstanding - diluted (in shares)	17,245,000	17,203,000	17,194,000	17,157,000	17,167,000	17,102,000	16,989,000	16,939,000	17,208,000	17,067,000	16,872,000
Diluted earnings per common share (in dollars per share)	$ 0.70	$ 0.72	$ 0.64	$ 0.64	$ 0.62	$ 0.60	$ 0.68	$ 0.65	$ 2.70	$ 2.54	$ 2.41
Antidilutive common stock equivalents									59,158	34,850	59,234