Loans Receivable, Financial Instruments Whose Contract Amounts Represent Credit Risk (Details) (USD $)	9 Months Ended	12 Months Ended
	Sep. 30, 2012	Dec. 31, 2011
Standby letters of credit [Member]
Financial instruments whose contract amount represents credit risk [Abstract]
Off-balance sheet credit risk	$ 16,365,000	$ 15,319,000
Home equity lines of Credit [Member]
Financial instruments whose contract amount represents credit risk [Abstract]
Off-balance sheet credit risk	14,026,000	14,623,000
Loan expiry period	10 years
Unadvanced construction commitments [Member]
Financial instruments whose contract amount represents credit risk [Abstract]
Off-balance sheet credit risk	11,946,000	18,014,000
Fixed rate loan commitments	7,359,000	1,059,000
Fixed interest rate, minimum (in hundredths)	2.75%	3.25%
Fixed interest rate, maximum (in hundredths)	4.125%	5.50%
Floating rate loan commitments	550,000	0
Mortgage loan commitments [Member]
Financial instruments whose contract amount represents credit risk [Abstract]
Off-balance sheet credit risk	7,909,000	1,059,000
Lines of credit [Member]
Financial instruments whose contract amount represents credit risk [Abstract]
Off-balance sheet credit risk	32,689,000	31,525,000
Loans sold with limited repurchase provision [Member]
Financial instruments whose contract amount represents credit risk [Abstract]
Off-balance sheet credit risk	31,358,000	17,558,000
Loans receivable held-for-sale, amount	$ 61,557,000	$ 43,403,000