Earnings Per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Earnings Per Share [Abstract]
Net income	$ 43,465	$ 40,824	$ 36,153
Less dividends and undistributed earnings allocated to participating securities	(126)	(152)	(156)
Net income applicable to common shareholders	$ 43,339	$ 40,672	$ 35,997
Weighted average common shares outstanding - basic (in shares)	16,879,000	16,689,000	16,506,000
Basic earnings per common share (in dollars per share)	$ 2.57	$ 2.44	$ 2.18
Less dividends and undistributed earnings allocated to participating securities	$ (126)	$ (151)	$ (155)
Net income applicable to common shareholders	$ 43,339	$ 40,673	$ 35,998
Dilutive effect of common stock equivalents (in shares)	188,000	183,000	158,000
Weighted average common shares outstanding - diluted (in shares)	17,067,000	16,872,000	16,664,000
Diluted earnings per common share (in dollars per share)	$ 2.54	$ 2.41	$ 2.16
Antidilutive common stock equivalents	34,850	59,234	23,286