Earnings Per Common Share - Basic and Diluted Earnings Per Common Share (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Earnings Per Share [Abstract]
Net income	$ 73,077	$ 66,704	$ 145,240	$ 127,892
Less: Preferred stock dividends	2,015	2,015	4,031	4,031
Net income available to common shareholders	71,062	64,689	141,209	123,861
Less: Earnings allocated to participating securities	247	247	484	473
Distributed earnings allocated to common stock	33,465	32,050	65,644	62,421
Undistributed earnings allocated to common stock	37,350	32,392	75,081	60,967
Net earnings allocated to common stock	$ 70,815	$ 64,442	$ 140,725	$ 123,388
Weighted-average shares outstanding for basic earnings per common share	63,118,785	61,551,473	63,106,656	61,128,725
Dilutive effect of stock compensation	831,938	915,083	760,331	902,024
Weighted-average shares outstanding for diluted earnings per common share	63,950,723	62,466,556	63,866,987	62,030,749