Allowance for Loan Losses and Credit Quality of Loans, Credit Quality by Loan Class (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Commercial Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	$ 1,726,583	$ 1,446,436
Commercial Loans [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	1,606,270	1,316,413
Commercial Loans [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	35,354	34,876
Commercial Loans [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	81,938	94,622
Commercial Loans [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	3,021	525
Commercial Loans [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	602,546	511,074
Commercial Loans [Member] | Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	565,546	470,332
Commercial Loans [Member] | Commercial [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	11,371	10,346
Commercial Loans [Member] | Commercial [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	22,656	29,940
Commercial Loans [Member] | Commercial [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	2,973	456
Commercial Loans [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	1,020,720	834,899
Commercial Loans [Member] | Commercial Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	948,966	758,673
Commercial Loans [Member] | Commercial Real Estate [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	23,967	24,478
Commercial Loans [Member] | Commercial Real Estate [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	47,787	51,748
Commercial Loans [Member] | Commercial Real Estate [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	0	0
Commercial Loans [Member] | Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	66,774	66,537
Commercial Loans [Member] | Agricultural [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	59,545	58,481
Commercial Loans [Member] | Agricultural [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	13	42
Commercial Loans [Member] | Agricultural [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	7,168	7,945
Commercial Loans [Member] | Agricultural [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	48	69
Commercial Loans [Member] | Agricultural Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	36,543	33,926
Commercial Loans [Member] | Agricultural Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	32,213	28,927
Commercial Loans [Member] | Agricultural Real Estate [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	3	10
Commercial Loans [Member] | Agricultural Real Estate [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	4,327	4,989
Commercial Loans [Member] | Agricultural Real Estate [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	0	0
Commercial Loans [Member] | Business Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	266,308	256,141
Commercial Loans [Member] | Business Banking [Member] | Non-classified [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	251,284	237,887
Commercial Loans [Member] | Business Banking [Member] | Classified [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	15,024	18,254
Consumer Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	1,607,780	1,516,115
Consumer Loans [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	1,596,096	1,503,879
Consumer Loans [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	11,684	12,236
Consumer Loans [Member] | Indirect [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	962,619	873,103
Consumer Loans [Member] | Indirect [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	959,938	870,270
Consumer Loans [Member] | Indirect [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	2,681	2,833
Consumer Loans [Member] | Home Equity [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	576,208	569,645
Consumer Loans [Member] | Home Equity [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	567,509	560,760
Consumer Loans [Member] | Home Equity [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	8,699	8,885
Consumer Loans [Member] | Direct [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	68,953	73,367
Consumer Loans [Member] | Direct [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	68,649	72,849
Consumer Loans [Member] | Direct [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	304	518
Residential Real Estate Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	650,448	581,511
Residential Real Estate Mortgages [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	639,638	571,704
Residential Real Estate Mortgages [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	$ 10,810	$ 9,807