Allowance for Credit Losses - Summary of Provision for Credit Losses (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Financing Receivable, Allowance for Credit Losses [Line Items]
Provision for non-covered loans									$ 25,640	$ 31,242	$ 42,943
Provision for covered loans										21,510	6,378
Total provision for loan losses									25,640	52,752	49,321
Provision for unfunded letters of credit									(88)	583	135
Total provision for credit losses	$ 5,200	$ 7,250	$ 7,405	$ 5,697	$ 15,364	$ 7,783	$ 6,026	$ 24,162	$ 25,552	$ 53,335	$ 49,456