Earnings Per Common Share - Basic and Diluted Earnings Per Common Share (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Earnings Per Share [Abstract]
Net income	$ 60,444	$ 58,669	$ 175,295	$ 177,764
Less: Preferred stock dividends	2,015	0	4,703	0
Net income available to common shareholders	58,429	58,669	170,592	177,764
Less: Earnings allocated to participating securities	214	188	621	564
Net earnings allocated to common stock	58,215	58,481	169,971	177,200
Distributed earnings allocated to common stock	30,202	29,430	88,935	87,005
Undistributed earnings allocated to common stock	28,013	29,051	81,036	90,195
Net earnings allocated to common stock	$ 58,215	$ 58,481	$ 169,971	$ 177,200
Weighted-average shares outstanding for basic earnings per common share	60,339,509	61,316,854	60,313,274	61,269,850
Dilutive effect of stock compensation	866,616	369,596	724,039	347,204
Weighted-average shares outstanding for diluted earnings per common share	61,206,125	61,686,450	61,037,313	61,617,054