Net Income Per Common Share - (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Basic
Net income applicable to common stock	$ 16,220	$ 15,535	$ 46,854	$ 43,985
Average common shares outstanding (shares)	40,265,941	31,526,423	34,521,255	31,486,767
Net income per common share - basic (usd per share)	$ 0.40	$ 0.49	$ 1.36	$ 1.40
Diluted
Net income applicable to common stock	$ 16,220	$ 15,535	$ 46,854	$ 43,985
Average common shares outstanding (shares)	40,265,941	31,526,423	34,521,255	31,486,767
Effect of dilutive stock-based compensation (shares)	252,472	192,106	277,863	207,834
Average common shares outstanding - diluted (shares)	40,518,413	31,718,529	34,799,118	31,694,601
Net income per common share - diluted (usd per share)	$ 0.40	$ 0.49	$ 1.35	$ 1.39