Earnings Per Common Share - Basic and Diluted Earnings Per Common Share (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Earnings Per Share [Abstract]
Net income	$ 80,219	$ 75,850	$ 220,542	$ 221,090
Less: Preferred stock dividends	2,016	2,016	6,047	6,047
Net income available to common shareholders	78,203	73,834	214,495	215,043
Less: Earnings allocated to participating securities	282	260	769	744
Distributed earnings allocated to common stock	33,918	33,030	100,203	98,674
Undistributed earnings allocated to common stock	44,003	40,544	113,523	115,625
Net earnings allocated to common stock	$ 77,921	$ 73,574	$ 213,726	$ 214,299
Weighted-average shares outstanding for basic earnings per common share	62,449,660	62,628,725	62,114,075	62,945,595
Dilutive effect of stock compensation	691,543	690,041	448,290	736,197
Weighted-average shares outstanding for diluted earnings per common share	63,141,203	63,318,766	62,562,365	63,681,792