Earnings Per Common Share - Basic and Diluted Earnings Per Common Share (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Earnings Per Share [Abstract]
Net income	$ 85,553	$ 71,507	$ 170,494	$ 140,323
Less: Preferred stock dividends	2,015	2,015	4,031	4,031
Net income available to common shareholders	83,538	69,492	166,463	136,292
Less: Earnings allocated to participating securities	436	252	871	487
Distributed earnings allocated to common stock	36,545	33,463	71,020	66,285
Undistributed earnings allocated to common stock	46,557	35,777	94,572	69,520
Net earnings allocated to common stock	$ 83,102	$ 69,240	$ 165,592	$ 135,805
Weighted-average shares outstanding for basic earnings per common share	64,061,264	61,959,411	63,900,620	61,944,438
Dilutive effect of stock compensation	974,067	497,532	988,198	267,632
Weighted-average shares outstanding for diluted earnings per common share	65,035,331	62,456,943	64,888,818	62,212,070