Net Income Per Common Share - Basic and Diluted Net Income Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Basic
Net income applicable to common stock	$ 38,415	$ 37,446	$ 46,625	$ 45,110	$ 44,420	$ 31,964	$ 36,710	$ 33,826	$ 167,596	$ 146,920	$ 92,188
Average common shares outstanding (shares)									58,046,716	52,492,104	46,874,502
Net income per common share - basic (usd per share)	$ 0.67	$ 0.65	$ 0.80	$ 0.77	$ 0.76	$ 0.61	$ 0.74	$ 0.69	$ 2.89	$ 2.80	$ 1.97
Diluted
Net income applicable to common stock	$ 38,415	$ 37,446	$ 46,625	$ 45,110	$ 44,420	$ 31,964	$ 36,710	$ 33,826	$ 167,596	$ 146,920	$ 92,188
Average common shares outstanding (shares)									58,046,716	52,492,104	46,874,502
Effect of dilutive stock-based compensation (shares)									179,970	134,746	127,014
Average common shares outstanding - diluted (shares)									58,226,686	52,626,850	47,001,516
Net income per common share - diluted (usd per share)	$ 0.67	$ 0.64	$ 0.80	$ 0.77	$ 0.76	$ 0.61	$ 0.74	$ 0.68	$ 2.88	$ 2.79	$ 1.96