Earnings Per Common Share - Basic and Diluted Earnings Per Common Share (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Earnings Per Share [Abstract]
Net income	$ 93,131	$ 80,219	$ 263,625	$ 220,542
Less: Preferred stock dividends	2,016	2,016	6,047	6,047
Net income available to common shareholders	91,115	78,203	257,578	214,495
Less: Earnings allocated to participating securities	475	282	1,346	769
Distributed earnings allocated to common stock	36,174	33,918	107,194	100,203
Undistributed earnings allocated to common stock	54,466	44,003	149,038	113,523
Net earnings allocated to common stock	$ 90,640	$ 77,921	$ 256,232	$ 213,726
Weighted-average shares outstanding for basic earnings per common share	63,667,356	62,449,660	63,822,011	62,114,075
Dilutive effect of stock compensation	897,945	691,543	957,337	448,290
Weighted-average shares outstanding for diluted earnings per common share	64,565,301	63,141,203	64,779,348	62,562,365