Allowance for Loan and Lease Losses and Credit Quality of Loans and Leases Impaired Loans and Reserve Allocations (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Financing Receivable, Impaired [Line Items]
Recorded Investment Balance (Book)	$ 500,000
Related Allowance	200,000	2,200,000
Average Recorded Investment	23,094,000	21,929,000	23,650,000
Interest Income Recognized Total	1,086,000	1,237,000	6,335,000
Interest Income Recognized Cash	1,086,000	1,237,000	6,335,000
Troubled Debt Restructured Loans Amount	4,000,000	1,000,000
Commercial Financing Receivable [Member]
Financing Receivable, Impaired [Line Items]
Troubled Debt Restructured Loans Amount	700,000
Modifications made to loans	700,000	300,000
Number of loans with modifications	3	1
Number of loans classified as troubled debt restructuring	2
Home Equity Financing Receivable [Member]
Financing Receivable, Impaired [Line Items]
Troubled Debt Restructured Loans Amount	600,000
Modifications made to loans	2,400,000
Number of loans with modifications	25
Number of loans classified as troubled debt restructuring	7
Commercial Portfolio Segment [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment Balance (Book)		25,364,000
Unpaid Principal Balance (Legal)		31,059,000
Financing Receivable	1,446,436,000	1,308,483,000
Commercial Portfolio Segment [Member] | Commercial Financing Receivable [Member]
Financing Receivable, Impaired [Line Items]
Financing Receivable	511,074,000	467,755,000
Commercial Portfolio Segment [Member] | Commercial Real Estate Other Receivable [Member]
Financing Receivable, Impaired [Line Items]
Financing Receivable	834,899,000	737,235,000
Commercial Portfolio Segment [Member] | Agricultural Financing Receivable [Member]
Financing Receivable, Impaired [Line Items]
Financing Receivable	66,537,000	67,556,000
Commercial Portfolio Segment [Member] | Agricultural Real Estate Financing Receivable [Member]
Financing Receivable, Impaired [Line Items]
Financing Receivable	33,926,000	35,937,000
Commercial Portfolio Segment [Member] | Small Business Financing Receivable [Member]
Financing Receivable, Impaired [Line Items]
Financing Receivable	256,141,000	271,888,000
Consumer Loans and Leases [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment Balance (Book)	22,427,000
Unpaid Principal Balance (Legal)	30,354,000
Related Allowance	175,000	2,211,000
Residential Real Estate Mortgages [Member]
Financing Receivable, Impaired [Line Items]
Financing Receivable	581,511,000	548,394,000
Troubled Debt Restructured Loans Amount	400,000
Modifications made to loans	800,000
Number of loans with modifications	4
Number of loans classified as troubled debt restructuring	2
With No Allowance Recorded [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment Balance (Book)	21,971,000	19,240,000
Unpaid Principal Balance (Legal)	29,546,000	23,595,000
Average Recorded Investment	20,798,000	16,127,000	16,509,000
Interest Income Recognized Total	914,000	902,000	6,210,000
Interest Income Recognized Cash	914,000	902,000	6,210,000
With No Allowance Recorded [Member] | Total Commercial Loans Receivable No Allowance [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment Balance (Book)	18,931,000	18,927,000
Unpaid Principal Balance (Legal)	26,318,000	23,256,000
With No Allowance Recorded [Member] | Commercial Portfolio Segment [Member] | Commercial Financing Receivable [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment Balance (Book)	1,243,000	2,112,000
Unpaid Principal Balance (Legal)	2,723,000	2,459,000
Average Recorded Investment	2,322,000	1,898,000	1,118,000
Interest Income Recognized Total	94,000	113,000	1,429,000
Interest Income Recognized Cash	94,000	113,000	1,429,000
With No Allowance Recorded [Member] | Commercial Portfolio Segment [Member] | Commercial Real Estate Other Receivable [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment Balance (Book)	4,868,000	5,687,000
Unpaid Principal Balance (Legal)	7,165,000	6,654,000
Average Recorded Investment	4,794,000	4,219,000	5,702,000
Interest Income Recognized Total	163,000	317,000	2,744,000
Interest Income Recognized Cash	163,000	317,000	2,744,000
With No Allowance Recorded [Member] | Commercial Portfolio Segment [Member] | Agricultural Financing Receivable [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment Balance (Book)	3,307,000	2,394,000
Unpaid Principal Balance (Legal)	4,166,000	2,865,000
Average Recorded Investment	3,013,000	2,990,000	1,606,000
Interest Income Recognized Total	133,000	82,000	531,000
Interest Income Recognized Cash	133,000	82,000	531,000
With No Allowance Recorded [Member] | Commercial Portfolio Segment [Member] | Agricultural Real Estate Financing Receivable [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment Balance (Book)	2,067,000	1,701,000
Unpaid Principal Balance (Legal)	2,288,000	1,883,000
Average Recorded Investment	1,719,000	1,929,000	1,853,000
Interest Income Recognized Total	109,000	150,000	589,000
Interest Income Recognized Cash	109,000	150,000	589,000
With No Allowance Recorded [Member] | Commercial Portfolio Segment [Member] | Small Business Financing Receivable [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment Balance (Book)	7,446,000	7,033,000
Unpaid Principal Balance (Legal)	9,976,000	9,395,000
Average Recorded Investment	6,121,000	4,959,000	6,231,000
Interest Income Recognized Total	266,000	234,000	917,000
Interest Income Recognized Cash	266,000	234,000	917,000
With No Allowance Recorded [Member] | Consumer Loans and Leases [Member] | Home Equity Financing Receivable [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment Balance (Book)	2,000,000	0
Unpaid Principal Balance (Legal)	2,103,000	0
Average Recorded Investment	1,904,000	0	0
Interest Income Recognized Total	91,000	0	0
Interest Income Recognized Cash	91,000	0	0
With No Allowance Recorded [Member] | Residential Real Estate Mortgages [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment Balance (Book)	1,040,000	313,000
Unpaid Principal Balance (Legal)	1,125,000	339,000
Average Recorded Investment	926,000	132,000	0
Interest Income Recognized Total	58,000	6,000	0
Interest Income Recognized Cash	58,000	6,000	0
With An Allowance Recorded [Member]
Financing Receivable, Impaired [Line Items]
Related Allowance	175,000	2,211,000
With An Allowance Recorded [Member] | Commercial Portfolio Segment [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment Balance (Book)	456,000	6,124,000
Unpaid Principal Balance (Legal)	808,000	7,464,000
Average Recorded Investment	2,295,000	5,802,000	7,141,000
Interest Income Recognized Total	172,000	335,000	125,000
Interest Income Recognized Cash	172,000	335,000	125,000
With An Allowance Recorded [Member] | Commercial Portfolio Segment [Member] | Commercial Financing Receivable [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment Balance (Book)	456,000	3,725,000
Unpaid Principal Balance (Legal)	808,000	4,762,000
Related Allowance	175,000	1,907,000
Average Recorded Investment	861,000	2,366,000	2,984,000
Interest Income Recognized Total	86,000	118,000	57,000
Interest Income Recognized Cash	86,000	118,000	57,000
With An Allowance Recorded [Member] | Commercial Portfolio Segment [Member] | Commercial Real Estate Other Receivable [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	287,000	1,234,000	1,551,000
Interest Income Recognized Total	0	0	0
Interest Income Recognized Cash	0	0	0
With An Allowance Recorded [Member] | Commercial Portfolio Segment [Member] | Agricultural Financing Receivable [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment Balance (Book)	0	1,671,000
Unpaid Principal Balance (Legal)	0	1,918,000
Related Allowance	0	281,000
Average Recorded Investment	791,000	1,386,000	2,046,000
Interest Income Recognized Total	68,000	150,000	63,000
Interest Income Recognized Cash	68,000	150,000	63,000
With An Allowance Recorded [Member] | Commercial Portfolio Segment [Member] | Agricultural Real Estate Financing Receivable [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment Balance (Book)	0	728,000
Unpaid Principal Balance (Legal)	0	784,000
Related Allowance	0	23,000
Average Recorded Investment	357,000	816,000	560,000
Interest Income Recognized Total	18,000	67,000	5,000
Interest Income Recognized Cash	$ 18,000	$ 67,000	$ 5,000