Loans and Other Repossessed Assets Acquired (Detail) - Summary of the loans that were restructured as TDRs (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2012	Sep. 30, 2011
Post-Modification - Rate	$ 3,986	$ 4,425	$ 2,471
Post-Modification - Structure	12,200	12,280	8,782
Increase to Allowance	540	269	594
Acquired covered loans [Member]
Post-Modification - Structure	5,131	2,612	4,908
Increase to Allowance	5,131	2,612	4,908
Residential Loans [Member] | Residential 1-4 Family [Member]
Post-Modification - Rate	288	543	294
Post-Modification - Structure	1,715	1,202	734
Increase to Allowance	93		101
Residential Loans [Member] | Residential Land [Member]
Post-Modification - Rate		61
Residential Loans [Member]
Post-Modification - Rate	288	604	294
Post-Modification - Structure	1,715	1,202	734
Increase to Allowance	93		101
Commercial Loan [Member] | Commercial Business [Member]
Post-Modification - Structure	1,813	1,296	1,113
Commercial Loan [Member] | Commercial Real Estate [Member]
Post-Modification - Structure	6,270	6,256	5,000
Increase to Allowance	122	12	142
Commercial Loan [Member] | Commercial Land [Member]
Post-Modification - Structure	2,192	2,351	1,719
Increase to Allowance	325	257	351
Commercial Loan [Member]
Post-Modification - Structure	10,275	9,903	7,832
Increase to Allowance	447	269	493
Consumer Loan [Member] | Home Equity Loans [Member]
Post-Modification - Rate	3,565	3,686	2,042
Post-Modification - Structure	210	1,175	216
Consumer Loan [Member] | Manufactured Housing [Member]
Post-Modification - Rate	133	135	135
Consumer Loan [Member]
Post-Modification - Rate	3,698	3,821	2,177
Post-Modification - Structure	$ 210	$ 1,175	$ 216