Earnings Per Common Share - Basic and Diluted Earnings Per Common Share (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Net income	$ 55,188	$ 61,033
Less: Preferred stock dividends and accretion	137
Net income available to common shareholders	55,051	61,033
Less: Earnings allocated to participating securities	197	190
Net earnings allocated to common stock	54,854	60,843
Distributed earnings allocated to common stock	28,675	28,152
Undistributed earnings allocated to common stock	26,179	32,691
Net earnings allocated to common stock	$ 54,854	$ 60,843
Weighted-average shares outstanding for basic earnings per common share	60,592,567	61,200,627
Dilutive effect of stock compensation	581,205	332,674
Weighted-average shares outstanding for diluted earnings per common share	61,173,772	61,533,301