Earnings Per Common Share - Basic and Diluted Earnings Per Common Share (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Earnings Per Share [Abstract]
Net income	$ 71,479	$ 73,077	$ 140,258	$ 145,240
Less: Preferred stock dividends	2,015	2,015	4,031	4,031
Net income available to common shareholders	69,464	71,062	136,227	141,209
Less: Earnings allocated to participating securities	252	247	487	484
Distributed earnings allocated to common stock	33,463	33,465	66,285	65,644
Undistributed earnings allocated to common stock	35,749	37,350	69,455	75,081
Net earnings allocated to common stock	$ 69,212	$ 70,815	$ 135,740	$ 140,725
Weighted-average shares outstanding for basic earnings per common share	61,959,411	63,118,785	61,944,438	63,106,656
Dilutive effect of stock compensation	538,217	831,938	387,096	760,331
Weighted-average shares outstanding for diluted earnings per common share	62,497,628	63,950,723	62,331,534	63,866,987