Allowance for Credit Losses, Loans by Class Modified as Troubled Debt Restructured Loans (Details) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2013 Loan	Mar. 31, 2012 Loan	Dec. 31, 2012 Loan
Financing Receivable, Modifications [Line Items]
Specific reserves	$ 444,000	$ 44,000	$ 401,000
Troubled debt restructured loans	2,100,000	1,300,000	2,600,000
Commitments to lend additional amounts to customers with outstanding loans that are classified as troubled debt restructurings	0	0	0
Period of modifications involving a reduction of stated interest rate of the loan	5 years	5 years
Loans by class modified as troubled debt restructured loans [Abstract]
Number of Loans	7	8	18
Pre-Modification Outstanding Recorded Investment	614,000	612,000	2,033,000
Post-Modification Outstanding Recorded Investment	597,000	600,000	1,969,000
Increase in allowance for loan losses due to TDR	61,000		53,000
TDR's charge-offs	17,000	12,000	64,000
Charge offs on troubled debt restructurings that subsequently defaulted	0	0	0
Period after which loan is considered to be in payment default	90 days
Minimum [Member]
Financing Receivable, Modifications [Line Items]
Period of modifications involving a reduction of stated interest rate of the loan			2 years
Period of modifications involving extension of maturity date	16 months	6 months	6 months
Maximum [Member]
Financing Receivable, Modifications [Line Items]
Period of modifications involving a reduction of stated interest rate of the loan			5 years
Period of modifications involving extension of maturity date	10 years	15 years	10 years
Performing [Member]
Financing Receivable, Modifications [Line Items]
Troubled debt restructured loans, performing	1,400,000	1,200,000	2,300,000
Commercial Real Estate [Member]
Loans by class modified as troubled debt restructured loans [Abstract]
Number of Loans		1	1
Pre-Modification Outstanding Recorded Investment		116,000	116,000
Post-Modification Outstanding Recorded Investment		116,000	116,000
Residential 1st Mortgages [Member]
Loans by class modified as troubled debt restructured loans [Abstract]
Number of Loans	4	3	2
Pre-Modification Outstanding Recorded Investment	306,000	116,000	216,000
Post-Modification Outstanding Recorded Investment	290,000	110,000	201,000
Home Equity Lines & Loans [Member]
Loans by class modified as troubled debt restructured loans [Abstract]
Number of Loans	1	1	7
Pre-Modification Outstanding Recorded Investment	16,000	74,000	529,000
Post-Modification Outstanding Recorded Investment	15,000	68,000	480,000
Agricultural [Member]
Loans by class modified as troubled debt restructured loans [Abstract]
Number of Loans		1	4
Pre-Modification Outstanding Recorded Investment		180,000	858,000
Post-Modification Outstanding Recorded Investment		180,000	858,000
Commercial [Member]
Loans by class modified as troubled debt restructured loans [Abstract]
Number of Loans	2	2	3
Pre-Modification Outstanding Recorded Investment	292,000	126,000	273,000
Post-Modification Outstanding Recorded Investment	292,000	126,000	273,000
Consumer & Other [Member]
Loans by class modified as troubled debt restructured loans [Abstract]
Number of Loans			1
Pre-Modification Outstanding Recorded Investment			41,000
Post-Modification Outstanding Recorded Investment			$ 41,000