FDIC loss share (expense) income (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012		Mar. 31, 2011
F D I C Loss Share Expense Income [Line Items]
(Amortization) accretion of indemnification asset	$ (29,375)		$ 25,796
80% mirror accounting on discount accretion on loans and unfunded commitments accounted for under ASC 310-20	(248)		(21,465)
80% mirror accounting on on provision for loan losses for reductions in expected cash flows that are reimbursable by the FDIC	13,422	[1]	12,445	[1]
Other	946		(741)
FDIC loss share (expense) income	$ (15,255)		$ 16,035

[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.