Allowance for Loan Losses and Credit Quality of Loans, Credit Quality by Loan Class (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Commercial Credit Exposure [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	$ 1,637,411	$ 1,446,436
Commercial Credit Exposure [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	1,515,732	1,316,413
Commercial Credit Exposure [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	50,552	34,876
Commercial Credit Exposure [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	68,347	94,622
Commercial Credit Exposure [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	2,780	525
Commercial Credit Exposure [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	561,481	511,074
Commercial Credit Exposure [Member] | Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	522,985	470,332
Commercial Credit Exposure [Member] | Commercial [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	18,401	10,346
Commercial Credit Exposure [Member] | Commercial [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	17,351	29,940
Commercial Credit Exposure [Member] | Commercial [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	2,744	456
Commercial Credit Exposure [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	974,795	834,899
Commercial Credit Exposure [Member] | Commercial Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	901,928	758,673
Commercial Credit Exposure [Member] | Commercial Real Estate [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	32,135	24,478
Commercial Credit Exposure [Member] | Commercial Real Estate [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	40,732	51,748
Commercial Credit Exposure [Member] | Commercial Real Estate [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	0	0
Commercial Credit Exposure [Member] | Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	63,758	66,537
Commercial Credit Exposure [Member] | Agricultural [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	57,347	58,481
Commercial Credit Exposure [Member] | Agricultural [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	13	42
Commercial Credit Exposure [Member] | Agricultural [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	6,362	7,945
Commercial Credit Exposure [Member] | Agricultural [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	36	69
Commercial Credit Exposure [Member] | Agricultural Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	37,377	33,926
Commercial Credit Exposure [Member] | Agricultural Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	33,472	28,927
Commercial Credit Exposure [Member] | Agricultural Real Estate [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	3	10
Commercial Credit Exposure [Member] | Agricultural Real Estate [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	3,902	4,989
Commercial Credit Exposure [Member] | Agricultural Real Estate [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	0	0
Commercial Credit Exposure [Member] | Business Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	365,960	256,141
Commercial Credit Exposure [Member] | Business Banking [Member] | Non-classified [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	342,528	237,887
Commercial Credit Exposure [Member] | Business Banking [Member] | Classified [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	23,432	18,254
Consumer Credit Exposure [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	1,623,138	1,516,115
Consumer Credit Exposure [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	1,612,098	1,503,879
Consumer Credit Exposure [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	11,040	12,236
Consumer Credit Exposure [Member] | Indirect [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	980,997	873,103
Consumer Credit Exposure [Member] | Indirect [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	978,235	870,270
Consumer Credit Exposure [Member] | Indirect [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	2,762	2,833
Consumer Credit Exposure [Member] | Home Equity Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	575,282	569,645
Consumer Credit Exposure [Member] | Home Equity Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	567,354	560,760
Consumer Credit Exposure [Member] | Home Equity Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	7,928	8,885
Consumer Credit Exposure [Member] | Direct [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	66,859	73,367
Consumer Credit Exposure [Member] | Direct [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	66,509	72,849
Consumer Credit Exposure [Member] | Direct [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	350	518
Residential Mortgage Credit Exposure [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	651,107	581,511
Residential Mortgage Credit Exposure [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	641,608	571,704
Residential Mortgage Credit Exposure [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	$ 9,499	$ 9,807