Loans and Other Repossessed Assets Acquired (Detail) - Loan portfolio by major category (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Sep. 30, 2010
Loans Receivable Gross	$ 2,495,324	$ 2,385,457	$ 2,355,334
Less: Allowance for loan losses	44,179	53,524	54,333	86,871
Net loans	2,451,145	2,331,933	2,301,001
Residential Loans [Member] | Residential 1-4 Family [Member]
Loans Receivable Gross	956,355	975,405	909,907
Residential Loans [Member] | Residential Construction [Member]
Loans Receivable Gross	22,439	15,117	16,431
Residential Loans [Member] | Residential Land [Member]
Loans Receivable Gross	52,739	41,612	40,725
Residential Loans [Member]
Loans Receivable Gross	1,031,533	1,032,134	967,063
Less: Allowance for loan losses	7,790	8,748	7,796	10,730
Commercial Loan [Member] | Commercial Business [Member]
Loans Receivable Gross	118,379	83,814	80,871
Commercial Loan [Member] | Commercial Real Estate [Member]
Loans Receivable Gross	491,567	456,541	471,296
Commercial Loan [Member] | Commercial Construction [Member]
Loans Receivable Gross	1,064	16,477	15,051
Commercial Loan [Member] | Commercial Land [Member]
Loans Receivable Gross	70,109	61,238	67,432
Commercial Loan [Member]
Loans Receivable Gross	681,119	618,070	634,650
Consumer Loan [Member] | Home Equity Loans [Member]
Loans Receivable Gross	384,664	357,270	369,213
Consumer Loan [Member] | Manufactured Housing [Member]
Loans Receivable Gross	280,100	275,275	276,047
Consumer Loan [Member] | Marine [Member]
Loans Receivable Gross	75,736	52,590	55,243
Consumer Loan [Member] | Other Consumer [Member]
Loans Receivable Gross	42,172	50,118	53,118
Consumer Loan [Member]
Loans Receivable Gross	782,672	735,253	753,621
Less: Allowance for loan losses	$ 20,403	$ 22,581	$ 21,923	$ 22,959