Earnings Per Common Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Numerator for basic and diluted earnings per common share-net income applicable to common shares									$ 24,292	$ 22,235	$ 18,047
Denominator:
Denominator for basic earnings per common share-weighted-average common shares, including participating securities	9,316	9,445	9,607	9,681	9,766	9,780	9,774	9,736	9,511	9,764	9,728
Effect of dilutive securities:
Employee stock options									111	87	51
Warrants									353	320	219
Dilutive potential common shares	9,801	9,903	10,066	10,108	10,198	10,212	10,156	10,105	464	407	270
Denominator for diluted earnings per common share									9,975	10,171	9,998
Basic earnings per common share	$ 0.68	$ 0.75	$ 0.59	$ 0.53	$ 0.52	$ 0.56	$ 0.63	$ 0.57	$ 2.55	$ 2.28	$ 1.86
Diluted earnings per common share	$ 0.65	$ 0.71	$ 0.57	$ 0.51	$ 0.50	$ 0.54	$ 0.60	$ 0.55	$ 2.44	$ 2.19	$ 1.81