Earnings Per Common Share - Basic and Diluted Earnings Per Common Share (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Earnings Per Share [Abstract]
Net income	$ 59,663	$ 58,062	$ 114,851	$ 119,095
Less: Preferred stock dividends	2,688		2,688
Net income available to common shareholders	56,975	58,062	112,163	119,095
Less: Earnings allocated to participating securities	209	185	407	376
Net earnings allocated to common stock	56,766	57,877	111,756	118,719
Distributed earnings allocated to common stock	30,058	29,424	58,733	57,575
Undistributed earnings allocated to common stock	26,708	28,453	53,023	61,144
Net earnings allocated to common stock	$ 56,766	$ 57,877	$ 111,756	$ 118,719
Weighted-average shares outstanding for basic earnings per common share	60,010,527	61,290,792	60,299,939	61,245,959
Dilutive effect of stock compensation	664,597	344,044	628,961	338,732
Weighted-average shares outstanding for diluted earnings per common share	60,675,124	61,634,836	60,928,900	61,584,691