Allowance for Loan Losses and Credit Quality of Loans, Impaired Loans (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Allowance for Loan Losses and Credit Quality of Loans and Leases [Abstract]
Impaired loans modified in TDR	$ 26,000,000	$ 22,400,000
Minimum balance for classified loans to be evaluated individually for impairment	500,000
Financing Receivable, Impaired [Line Items]
Recorded Investment Balance (Book)	8,400,000
With No Allowance Recorded [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment Balance (Book)	17,598,000	21,971,000
Unpaid Principal Balance (Legal)	21,940,000	29,546,000
Average Recorded Investment	21,429,000	20,798,000	16,127,000
Interest Income Recognized Accrual	915,000	914,000	902,000
Interest Income Recognized Cash	915,000	914,000	902,000
With No Allowance Recorded [Member] | Commercial Loans [Member] | Commercial [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment Balance (Book)	650,000	1,243,000
Unpaid Principal Balance (Legal)	709,000	2,723,000
Average Recorded Investment	1,421,000	2,322,000	1,898,000
Interest Income Recognized Accrual	25,000	94,000	113,000
Interest Income Recognized Cash	25,000	94,000	113,000
With No Allowance Recorded [Member] | Commercial Loans [Member] | Commercial Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment Balance (Book)	3,909,000	4,868,000
Unpaid Principal Balance (Legal)	4,753,000	7,165,000
Average Recorded Investment	6,167,000	4,794,000	4,219,000
Interest Income Recognized Accrual	70,000	163,000	317,000
Interest Income Recognized Cash	70,000	163,000	317,000
With No Allowance Recorded [Member] | Commercial Loans [Member] | Agricultural [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment Balance (Book)	699,000	3,307,000
Unpaid Principal Balance (Legal)	1,019,000	4,166,000
Average Recorded Investment	2,611,000	3,013,000	2,990,000
Interest Income Recognized Accrual	368,000	133,000	82,000
Interest Income Recognized Cash	368,000	133,000	82,000
With No Allowance Recorded [Member] | Commercial Loans [Member] | Agricultural Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment Balance (Book)	1,038,000	2,067,000
Unpaid Principal Balance (Legal)	1,225,000	2,288,000
Average Recorded Investment	1,575,000	1,719,000	1,929,000
Interest Income Recognized Accrual	86,000	109,000	150,000
Interest Income Recognized Cash	86,000	109,000	150,000
With No Allowance Recorded [Member] | Commercial Loans [Member] | Business Banking [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment Balance (Book)	6,738,000	7,446,000
Unpaid Principal Balance (Legal)	9,269,000	9,976,000
Average Recorded Investment	6,636,000	6,121,000	4,959,000
Interest Income Recognized Accrual	227,000	266,000	234,000
Interest Income Recognized Cash	227,000	266,000	234,000
With No Allowance Recorded [Member] | Commercial Loans [Member] | Total Commercial Loans [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment Balance (Book)	13,034,000	18,931,000
Unpaid Principal Balance (Legal)	16,975,000	26,318,000
With No Allowance Recorded [Member] | Consumer Loans [Member] | Home Equity [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment Balance (Book)	2,553,000	2,000,000
Unpaid Principal Balance (Legal)	2,657,000	2,103,000
Average Recorded Investment	1,877,000	1,904,000	0
Interest Income Recognized Accrual	66,000	91,000	0
Interest Income Recognized Cash	66,000	91,000	0
With No Allowance Recorded [Member] | Residential Real Estate Mortgages [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment Balance (Book)	2,011,000	1,040,000
Unpaid Principal Balance (Legal)	2,308,000	1,125,000
Average Recorded Investment	1,143,000	926,000	132,000
Interest Income Recognized Accrual	73,000	58,000	6,000
Interest Income Recognized Cash	73,000	58,000	6,000
With An Allowance Recorded [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment Balance (Book)	26,001,000	22,427,000
Unpaid Principal Balance (Legal)	31,969,000	30,354,000
Related Allowance	2,848,000	175,000
Average Recorded Investment	25,985,000	23,094,000	21,929,000
Interest Income Recognized Accrual	958,000	1,086,000	1,237,000
Interest Income Recognized Cash	958,000	1,086,000	1,237,000
With An Allowance Recorded [Member] | Commercial Loans [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment Balance (Book)	8,403,000	456,000
Unpaid Principal Balance (Legal)	10,029,000	808,000
Related Allowance	2,848,000	175,000
Average Recorded Investment	4,556,000	2,295,000	5,802,000
Interest Income Recognized Accrual	43,000	172,000	335,000
Interest Income Recognized Cash	43,000	172,000	335,000
With An Allowance Recorded [Member] | Commercial Loans [Member] | Commercial [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment Balance (Book)	4,335,000	456,000
Unpaid Principal Balance (Legal)	4,340,000	808,000
Related Allowance	2,241,000	175,000
Average Recorded Investment	4,217,000	861,000	2,366,000
Interest Income Recognized Accrual	43,000	86,000	118,000
Interest Income Recognized Cash	43,000	86,000	118,000
With An Allowance Recorded [Member] | Commercial Loans [Member] | Commercial Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment Balance (Book)	4,068,000	0
Unpaid Principal Balance (Legal)	5,689,000	0
Related Allowance	607,000	0
Average Recorded Investment	339,000	287,000	1,234,000
Interest Income Recognized Accrual	0	0	0
Interest Income Recognized Cash	0	0	0
With An Allowance Recorded [Member] | Commercial Loans [Member] | Agricultural [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment Balance (Book)	0	0
Unpaid Principal Balance (Legal)	0	0
Related Allowance	0	0
Average Recorded Investment	0	791,000	1,386,000
Interest Income Recognized Accrual	0	68,000	150,000
Interest Income Recognized Cash	0	68,000	150,000
With An Allowance Recorded [Member] | Commercial Loans [Member] | Agricultural Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment Balance (Book)	0	0
Unpaid Principal Balance (Legal)	0	0
Related Allowance	0	0
Average Recorded Investment	0	357,000	816,000
Interest Income Recognized Accrual	0	18,000	67,000
Interest Income Recognized Cash	$ 0	$ 18,000	$ 67,000