Net Income Per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Basic
Net income applicable to common stock	$ 21,160	$ 16,220	$ 15,394	$ 15,240	$ 15,597	$ 15,535	$ 14,853	$ 13,597	$ 68,014	$ 59,582	$ 33,487
Average common shares outstanding (shares)									35,971,877	31,499,498	27,269,613
Net income per common share - basic (usd per share)	$ 0.53	$ 0.40	$ 0.49	$ 0.48	$ 0.49	$ 0.49	$ 0.47	$ 0.43	$ 1.89	$ 1.89	$ 1.23
Diluted
Net income applicable to common stock	$ 21,160	$ 16,220	$ 15,394	$ 15,240	$ 15,597	$ 15,535	$ 14,853	$ 13,597	$ 68,014	$ 59,582	$ 33,487
Average common shares outstanding (shares)									35,971,877	31,499,498	27,269,613
Effect of dilutive stock-based compensation (shares)									255,562	260,149	191,144
Average common shares outstanding - diluted (shares)									36,227,439	31,759,647	27,460,757
Net income per common share - diluted (usd per share)	$ 0.52	$ 0.40	$ 0.48	$ 0.48	$ 0.49	$ 0.49	$ 0.47	$ 0.43	$ 1.88	$ 1.88	$ 1.22