FDIC Indemnification Asset (Detail) - Schedule of changes in FDIC indemnification asset (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Balance	$ 80,268
Payments from FDIC for losses	21,200
Amortization of potential impairment	3,806	0
Balance	58,917	46,272
Gross Receivable [Member]
Balance	80,801	51,213
Increase due to credit losses recorded on FDIC covered loans	3,339	0
Payments from FDIC for losses	(20,738)	(4,760)
Amortization of potential impairment	(3,806)	0
Changes due to change in cash flow assumptions on OREO	(228)	(4)
Discount accretion	0	0
Balance	59,368	46,449
Discount [Member]
Balance	(533)	(192)
Increase due to credit losses recorded on FDIC covered loans	0	0
Payments from FDIC for losses	0	0
Amortization of potential impairment	0	0
Changes due to change in cash flow assumptions on OREO	0	0
Discount accretion	82	15
Balance	(451)	(177)
Net Receivable [Member]
Balance	80,268	51,021
Increase due to credit losses recorded on FDIC covered loans	3,339	0
Payments from FDIC for losses	(20,738)	(4,760)
Amortization of potential impairment	(3,806)	0
Changes due to change in cash flow assumptions on OREO	(228)	(4)
Discount accretion	82	15
Balance	$ 58,917	$ 46,272