Net Income Per Common Share - Basic and Diluted Net Income Per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Basic
Net income applicable to common stock	$ 45,110	$ 33,826
Average common shares outstanding (shares)	58,585,517	49,356,417
Net income per common share - basic (usd per share)	$ 0.77	$ 0.69
Diluted
Net income applicable to common stock	$ 45,110	$ 33,826
Average common shares outstanding (shares)	58,585,517	49,356,417
Effect of dilutive stock-based compensation (shares)	145,018	146,533
Average common shares outstanding - diluted (shares)	58,730,535	49,502,950
Net income per common share - diluted (usd per share)	$ 0.77	$ 0.68