Loans (Narrative) (Detail) (USD $)	1 Months Ended			6 Months Ended		12 Months Ended
	Jun. 30, 2012	Dec. 31, 2011	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011
Covered loans acquired in FDIC-assisted transactions	$ 601,700,000	$ 571,500,000	$ 486,500,000
Nonaccrual loans	200,000			200,000
Loan-to-value ratio	110.00%			110.00%
Modified loans	14,300,000		37,200,000	14,300,000	37,200,000
Troubled debt restructurings	28,200,000	26,100,000		28,200,000		26,100,000
Troubled debt restructurings, previous charge-offs				2,000,000		1,700,000
Allowance for loan losses allocated to troubled debt restructurings				868,000		2,700,000
Troubled debt restructurings, provision for loan loss expense				1,400,000	1,600,000	2,400,000
Troubled Debt Restructuring [Member]
Nonaccrual loans	$ 100,000			$ 100,000