Financial Instruments with Off-Balance Sheet Risk and Derivative Transactions (Details) (USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2013 institution	Dec. 31, 2012 institution
Not designated as hedging instruments
Financial Instruments with Off-Balance Sheet Risk and Derivative Transactions
Asset Derivatives, Fair Value	$ 1,656,000	$ 1,869,000
Liability Derivatives, Fair Value	1,197,000	1,354,000
Interest rate swap agreements net of swap credit valuation
Financial Instruments with Off-Balance Sheet Risk and Derivative Transactions
Investment securities pledged with financial institutions, dollars	7,000,000	7,400,000
Investment securities pledged with financial institutions, number	3	2
Interest rate swap agreements net of swap credit valuation | Not designated as hedging instruments
Financial Instruments with Off-Balance Sheet Risk and Derivative Transactions
Weighted average maturity (in years)	1 year 5 months 26 days	1 year 3 months 18 days
Notional or Contractual Amount	91,879,000	82,097,000
Asset Derivatives, Fair Value	1,164,000	1,302,000
Liability Derivatives, Fair Value	1,197,000	1,349,000
Commitments | Not designated as hedging instruments
Financial Instruments with Off-Balance Sheet Risk and Derivative Transactions
Notional or Contractual Amount	233,514,000	226,135,000
Asset Derivatives, Fair Value	492,000	567,000
Forward contracts | Not designated as hedging instruments
Financial Instruments with Off-Balance Sheet Risk and Derivative Transactions
Notional or Contractual Amount	27,000,000	28,000,000
Liability Derivatives, Fair Value		$ 5,000