Net Income Per Common Share - Basic and Diluted Net Income Per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Basic
Net income applicable to common stock	$ 31,964	$ 26,421	$ 102,500	$ 75,677
Average common shares outstanding (shares)	52,472,971	49,316,572	50,425,797	46,050,250
Net income per common share - basic (usd per share)	$ 0.61	$ 0.54	$ 2.03	$ 1.64
Diluted
Net income applicable to common stock	$ 31,964	$ 26,421	$ 102,500	$ 75,677
Average common shares outstanding (shares)	52,472,971	49,316,572	50,425,797	46,050,250
Effect of dilutive stock-based compensation (shares)	136,931	118,653	127,395	117,891
Average common shares outstanding - diluted (shares)	52,609,902	49,435,225	50,553,192	46,168,141
Net income per common share - diluted (usd per share)	$ 0.61	$ 0.53	$ 2.03	$ 1.64