Fair Value of Financial Instruments (Detail) - Carrying value and fair value of the financial instruments (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012		Dec. 31, 2011		Sep. 30, 2011	Dec. 31, 2010
Assets
Cash and cash equivalents	$ 86,417		$ 76,675		$ 85,937	$ 53,404
Cash and cash equivalents	86,417		76,675
Securities available for sale	236,048		404,550		412,108
Securities available for sale	236,048		404,550
Securities held to maturity	17,331		20,486		21,671
Securities held to maturity	19,830		23,242
Nonmarketable securities	23,254		32,694		35,782
Nonmarketable securities	23,254		32,694
Net loans	2,528,018		2,331,933		2,301,001
Net loans	2,589,327		2,427,526
Loans held for sale	53,761		48,303		94,872
Loans held for sale	53,761		48,303
FDIC indemnification asset, net	75,017		51,021		50,465
FDIC indemnification asset, net	75,017		51,021
Other repossessed assets acquired1	21,579	[1]	20,487	[1]
Other repossessed assets acquired1	21,579	[1]	20,487	[1]
Residential mortgage servicing rights1	12,504	[1]	10,663	[1]
Residential mortgage servicing rights1	12,504	[1]	10,663	[1]
Accrued interest receivable1	9,654	[1]	8,759	[1]
Accrued interest receivable1	9,654	[1]	8,759	[1]
Derivative financial instruments1	2,887	[1]	2,238	[1]
Derivative financial instruments1	2,887	[1]	2,238	[1]
Liabilities
Deposits	2,616,757		2,239,198		2,302,857
Deposits	2,632,401		2,253,138
Advances from FHLB	253,000		561,000		558,000
Advances from FHLB	282,373		598,616
Long-term debt	47,204		47,204		47,204
Long-term debt	46,286		43,487
FDIC true-up liability2	3,599	[2]	0	[2]
FDIC true-up liability2	3,599	[2]	0	[2]
Accrued interest payable2	6,043	[2]	8,095	[2]
Accrued interest payable2	$ 6,043	[2]	$ 8,095	[2]

[1] Included as part of Other Assets in the Consolidated Balance Sheets.

[2] Included as part of Other Liabilities in the Consolidated Balance Sheets.