Allowance for Loan Losses and Credit Quality of Loans, Impaired Loans (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Allowance for Loan Losses and Credit Quality of Loans [Abstract]
Minimum balance for classified loans to be evaluated individually for impairment	$ 500		$ 500
Financing Receivable, Impaired [Line Items]
Recorded Investment Balance (Book)	25,932		25,932		22,427
Unpaid Principal Balance (Legal)	31,947		31,947		30,354
Related Allowance	2,720		2,720		175
Average Recorded Investment	26,715	24,859	26,397	23,181
Interest Income Recognized Accrual	218	283	591	805
Interest Income Recognized Cash	218	283	591	805
With No Allowance Recorded [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment Balance (Book)	19,868		19,868		21,971
Unpaid Principal Balance (Legal)	25,834		25,834		29,546
Average Recorded Investment	20,624	24,316	22,220	20,278
Interest Income Recognized Accrual	184	263	548	651
Interest Income Recognized Cash	184	263	548	651
With No Allowance Recorded [Member] | Commercial Loans [Member] | Commercial [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment Balance (Book)	851		851		1,243
Unpaid Principal Balance (Legal)	1,257		1,257		2,723
Average Recorded Investment	854	1,794	1,319	2,625
Interest Income Recognized Accrual	9	3	23	76
Interest Income Recognized Cash	9	3	23	76
With No Allowance Recorded [Member] | Commercial Loans [Member] | Commercial Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment Balance (Book)	6,432		6,432		4,868
Unpaid Principal Balance (Legal)	8,396		8,396		7,165
Average Recorded Investment	6,732	6,106	6,564	4,728
Interest Income Recognized Accrual	16	14	48	59
Interest Income Recognized Cash	16	14	48	59
With No Allowance Recorded [Member] | Commercial Loans [Member] | Agricultural [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment Balance (Book)	2,587		2,587		3,307
Unpaid Principal Balance (Legal)	3,567		3,567		4,166
Average Recorded Investment	2,627	3,516	2,873	2,903
Interest Income Recognized Accrual	51	59	159	104
Interest Income Recognized Cash	51	59	159	104
With No Allowance Recorded [Member] | Commercial Loans [Member] | Agricultural Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment Balance (Book)	1,195		1,195		2,067
Unpaid Principal Balance (Legal)	1,382		1,382		2,288
Average Recorded Investment	1,348	1,874	1,734	1,622
Interest Income Recognized Accrual	3	34	13	72
Interest Income Recognized Cash	3	34	13	72
With No Allowance Recorded [Member] | Commercial Loans [Member] | Business Banking [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment Balance (Book)	5,921		5,921		7,446
Unpaid Principal Balance (Legal)	8,078		8,078		9,976
Average Recorded Investment	6,169	7,655	6,824	5,662
Interest Income Recognized Accrual	70	101	166	203
Interest Income Recognized Cash	70	101	166	203
With No Allowance Recorded [Member] | Commercial Loans [Member] | Total Commercial Loans [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment Balance (Book)	16,986		16,986		18,931
Unpaid Principal Balance (Legal)	22,680		22,680		26,318
With No Allowance Recorded [Member] | Consumer Loans [Member] | Home Equity [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment Balance (Book)	1,777		1,777		2,000
Unpaid Principal Balance (Legal)	1,879		1,879		2,103
Average Recorded Investment	1,783	2,312	1,840	1,851
Interest Income Recognized Accrual	18	26	66	84
Interest Income Recognized Cash	18	26	66	84
With No Allowance Recorded [Member] | Residential Real Estate Mortgages [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment Balance (Book)	1,105		1,105		1,040
Unpaid Principal Balance (Legal)	1,275		1,275		1,125
Average Recorded Investment	1,111	1,059	1,066	887
Interest Income Recognized Accrual	17	26	73	53
Interest Income Recognized Cash	17	26	73	53
With An Allowance Recorded [Member] | Commercial Loans [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment Balance (Book)	6,064		6,064		456
Unpaid Principal Balance (Legal)	6,113		6,113		808
Related Allowance	2,720		2,720		175
Average Recorded Investment	6,091	543	4,178	2,903
Interest Income Recognized Accrual	34	20	43	154
Interest Income Recognized Cash	34	20	43	154
With An Allowance Recorded [Member] | Commercial Loans [Member] | Commercial [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment Balance (Book)	6,064		6,064		456
Unpaid Principal Balance (Legal)	6,113		6,113		808
Related Allowance	2,720		2,720		175
Average Recorded Investment	6,091	520	4,178	991
Interest Income Recognized Accrual	34	19	43	68
Interest Income Recognized Cash	34	19	43	68
With An Allowance Recorded [Member] | Commercial Loans [Member] | Commercial Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment Balance (Book)	0		0		0
Unpaid Principal Balance (Legal)	0		0		0
Related Allowance	0		0		0
Average Recorded Investment	0	0	0	382
Interest Income Recognized Accrual	0	0	0	0
Interest Income Recognized Cash	0	0	0	0
With An Allowance Recorded [Member] | Commercial Loans [Member] | Agricultural [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment Balance (Book)	0		0		0
Unpaid Principal Balance (Legal)	0		0		0
Related Allowance	0		0		0
Average Recorded Investment	0	23	0	1,055
Interest Income Recognized Accrual	0	1	0	68
Interest Income Recognized Cash	0	1	0	68
With An Allowance Recorded [Member] | Commercial Loans [Member] | Agricultural Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment Balance (Book)	0		0		0
Unpaid Principal Balance (Legal)	0		0		0
Related Allowance	0		0		0
Average Recorded Investment	0	0	0	475
Interest Income Recognized Accrual	0	0	0	18
Interest Income Recognized Cash	$ 0	$ 0	$ 0	$ 18