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, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Basic
Net income applicable to common stock	$ 37,446	$ 46,625	$ 45,110	$ 31,964	$ 36,710	$ 33,826	$ 129,181	$ 102,500
Average common shares outstanding (shares)	58,003,215			52,472,971			58,347,840	50,425,797
Net income per common share - basic (usd per share)	$ 0.65			$ 0.61			$ 2.21	$ 2.03
Diluted
Net income applicable to common stock	$ 37,446	$ 46,625	$ 45,110	$ 31,964	$ 36,710	$ 33,826	$ 129,181	$ 102,500
Average common shares outstanding (shares)	58,003,215			52,472,971			58,347,840	50,425,797
Effect of dilutive stock-based compensation (shares)	189,204			136,931			160,742	127,395
Average common shares outstanding - diluted (shares)	58,192,419			52,609,902			58,508,582	50,553,192
Net income per common share - diluted (usd per share)	$ 0.64			$ 0.61			$ 2.21	$ 2.03