Loans and Other Repossessed Assets Acquired (Detail) - Defaulted TDRs With Structure Or Rate Modifications (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2012	Sep. 30, 2011
Pre-default balance	$ 625	$ 3,338	$ 4,359
Covered loans included above	0	300	2,587
Performing Financing Receivable [Member] | Residential Loans [Member] | Residential 1-4 Family [Member]
Pre-default balance	0	0	0
Performing Financing Receivable [Member] | Commercial Loan [Member] | Commercial Business [Member]
Pre-default balance	0	0	0
Performing Financing Receivable [Member] | Commercial Loan [Member] | Commercial Real Estate [Member]
Pre-default balance	0	662	0
Performing Financing Receivable [Member] | Commercial Loan [Member] | Commercial Land [Member]
Pre-default balance	0	0	0
Performing Financing Receivable [Member] | Commercial Loan [Member]
Pre-default balance	0	662	0
Performing Financing Receivable [Member] | Consumer Loan [Member] | Home Equity Loans [Member]
Pre-default balance	0	0	0
Performing Financing Receivable [Member] | Consumer Loan [Member]
Pre-default balance	0	0	0
Performing Financing Receivable [Member]
Pre-default balance	0	662	0
Covered loans included above	0	0	0
Nonperforming Financing Receivable [Member] | Residential Loans [Member] | Residential 1-4 Family [Member]
Pre-default balance	0	0	294
Nonperforming Financing Receivable [Member] | Commercial Loan [Member] | Commercial Business [Member]
Pre-default balance	0	0	1,113
Nonperforming Financing Receivable [Member] | Commercial Loan [Member] | Commercial Real Estate [Member]
Pre-default balance	625	1,289	2,105
Nonperforming Financing Receivable [Member] | Commercial Loan [Member] | Commercial Land [Member]
Pre-default balance	0	0	522
Nonperforming Financing Receivable [Member] | Commercial Loan [Member]
Pre-default balance	625	1,289	3,740
Nonperforming Financing Receivable [Member] | Consumer Loan [Member] | Home Equity Loans [Member]
Pre-default balance	0	1,387	325
Nonperforming Financing Receivable [Member] | Consumer Loan [Member]
Pre-default balance	0	1,387	325
Nonperforming Financing Receivable [Member]
Pre-default balance	625	2,676	4,359
Covered loans included above	0	300	2,587
Residential Loans [Member] | Residential 1-4 Family [Member]
Pre-default balance	0	0	294
Commercial Loan [Member] | Commercial Business [Member]
Pre-default balance	0	0	1,113
Commercial Loan [Member] | Commercial Real Estate [Member]
Pre-default balance	625	1,951	2,105
Commercial Loan [Member] | Commercial Land [Member]
Pre-default balance	0	0	522
Commercial Loan [Member]
Pre-default balance	625	1,951	3,740
Consumer Loan [Member] | Home Equity Loans [Member]
Pre-default balance	0	1,387	325
Consumer Loan [Member]
Pre-default balance	$ 0	$ 1,387	$ 325