Activity in the FDIC loss share indemnification asset (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012		Mar. 31, 2011
Loss Share Indemnification Asset [Line Items]
Beginning Balance	$ 1,915,128		$ 2,410,219
Accretion of loss share indemnification asset, net	(29,375)		25,796
Credit impairment losses to be covered under loss sharing agreements	13,422	[1]	12,445	[1]
Decrease due to reciprocal accounting on the discount accreation for loans and unfunded commitments accounted for under ASC Subtopic 310-20	(248)		(21,465)
Payments received from FDIC under loss sharing agreements	(20,896)		(583)
Other adjustments attributable to FDIC loss sharing agreements	2,326		(107)
Ending Balance	$ 1,880,357		$ 2,426,305

[1] Reductions in expected cash flows for ASC 310-30 loans, which may impact the provision for loan losses, may consider reductions in both principal and interest cash flow expectations. The amount covered under the FDIC loss sharing agreements for interest not collected from borrowers is limited under the agreements (approximately 90 days); accordingly, these amounts are not subject fully to the 80% mirror accounting.