Income Tax (Detail) - Net tax effects of temporary differences between the carrying amounts of assets and liabilities (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Sep. 30, 2010
Deferred tax assets
Loan loss allowances deferred for tax purposes	$ 15,633	$ 20,396	$ 20,642	$ 31,615
Expenses not deducted under economic performance rules	2,650	2,672	2,601	2,837
Unrealized loss (gain) on securities available for sale	1,067	1,208	(2,179)	(3,527)
Post retirement benefits	901	932	931	768
Net operating loss carryforward	326	2,986	4,489	1,607
Book over tax basis on intangibles	229	79	64	501
Nondeductible loss on bulk loan sale	0	0	7,738	0
Federal credits	0	628	1,459	0
Charitable contribution carryforward	0	478	671	566
Other	2,786	3,948	3,622	892
Total gross deferred tax assets	23,592	33,327	40,038	35,259
Deferred tax liabilities
Deferred gain on FDIC transaction	15,273	14,705	14,915	17,115
Excess carrying value of assets acquired for financial reporting purposes over tax basis	6,877	6,708	6,839	6,898
Loan fee income adjustments for tax purposes	3,016	3,419	4,516	3,783
Expenses deducted under economic performance rules	603	736	875	895
FHLB stock dividends deferred for tax purposes	338	1,263	1,384	1,671
Other	1,132	1,097	671	883
Total gross deferred tax liabilities	27,239	27,928	29,200	31,245
Net deferred tax (liability) asset	$ (3,647)	$ 5,399	$ 10,838	$ 4,014