Allowance for Loan Losses and Credit Quality of Loans, Credit Quality by Loan Class (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012 Commercial Credit Exposure [Member]	Mar. 31, 2013 Commercial Credit Exposure [Member] ACQUIRED [Member]	Mar. 31, 2013 Commercial Credit Exposure [Member] ORIGINATED [Member]	Dec. 31, 2012 Commercial Credit Exposure [Member] Pass [Member]	Mar. 31, 2013 Commercial Credit Exposure [Member] Pass [Member] ACQUIRED [Member]	Mar. 31, 2013 Commercial Credit Exposure [Member] Pass [Member] ORIGINATED [Member]	Dec. 31, 2012 Commercial Credit Exposure [Member] Special Mention [Member]	Mar. 31, 2013 Commercial Credit Exposure [Member] Special Mention [Member] ACQUIRED [Member]	Mar. 31, 2013 Commercial Credit Exposure [Member] Special Mention [Member] ORIGINATED [Member]	Dec. 31, 2012 Commercial Credit Exposure [Member] Substandard [Member]	Mar. 31, 2013 Commercial Credit Exposure [Member] Substandard [Member] ACQUIRED [Member]	Mar. 31, 2013 Commercial Credit Exposure [Member] Substandard [Member] ORIGINATED [Member]	Dec. 31, 2012 Commercial Credit Exposure [Member] Doubtful [Member]	Mar. 31, 2013 Commercial Credit Exposure [Member] Doubtful [Member] ACQUIRED [Member]	Mar. 31, 2013 Commercial Credit Exposure [Member] Doubtful [Member] ORIGINATED [Member]	Dec. 31, 2012 Commercial Credit Exposure [Member] Commercial [Member]	Mar. 31, 2013 Commercial Credit Exposure [Member] Commercial [Member] ACQUIRED [Member]	Mar. 31, 2013 Commercial Credit Exposure [Member] Commercial [Member] ORIGINATED [Member]	Dec. 31, 2012 Commercial Credit Exposure [Member] Commercial [Member] Pass [Member]	Mar. 31, 2013 Commercial Credit Exposure [Member] Commercial [Member] Pass [Member] ACQUIRED [Member]	Mar. 31, 2013 Commercial Credit Exposure [Member] Commercial [Member] Pass [Member] ORIGINATED [Member]	Dec. 31, 2012 Commercial Credit Exposure [Member] Commercial [Member] Special Mention [Member]	Mar. 31, 2013 Commercial Credit Exposure [Member] Commercial [Member] Special Mention [Member] ACQUIRED [Member]	Mar. 31, 2013 Commercial Credit Exposure [Member] Commercial [Member] Special Mention [Member] ORIGINATED [Member]	Dec. 31, 2012 Commercial Credit Exposure [Member] Commercial [Member] Substandard [Member]	Mar. 31, 2013 Commercial Credit Exposure [Member] Commercial [Member] Substandard [Member] ACQUIRED [Member]	Mar. 31, 2013 Commercial Credit Exposure [Member] Commercial [Member] Substandard [Member] ORIGINATED [Member]	Dec. 31, 2012 Commercial Credit Exposure [Member] Commercial [Member] Doubtful [Member]	Mar. 31, 2013 Commercial Credit Exposure [Member] Commercial [Member] Doubtful [Member] ACQUIRED [Member]	Mar. 31, 2013 Commercial Credit Exposure [Member] Commercial [Member] Doubtful [Member] ORIGINATED [Member]	Dec. 31, 2012 Commercial Credit Exposure [Member] Commercial Real Estate [Member]	Mar. 31, 2013 Commercial Credit Exposure [Member] Commercial Real Estate [Member] ACQUIRED [Member]	Mar. 31, 2013 Commercial Credit Exposure [Member] Commercial Real Estate [Member] ORIGINATED [Member]	Dec. 31, 2012 Commercial Credit Exposure [Member] Commercial Real Estate [Member] Pass [Member]	Mar. 31, 2013 Commercial Credit Exposure [Member] Commercial Real Estate [Member] Pass [Member] ACQUIRED [Member]	Mar. 31, 2013 Commercial Credit Exposure [Member] Commercial Real Estate [Member] Pass [Member] ORIGINATED [Member]	Dec. 31, 2012 Commercial Credit Exposure [Member] Commercial Real Estate [Member] Special Mention [Member]	Mar. 31, 2013 Commercial Credit Exposure [Member] Commercial Real Estate [Member] Special Mention [Member] ACQUIRED [Member]	Mar. 31, 2013 Commercial Credit Exposure [Member] Commercial Real Estate [Member] Special Mention [Member] ORIGINATED [Member]	Dec. 31, 2012 Commercial Credit Exposure [Member] Commercial Real Estate [Member] Substandard [Member]	Mar. 31, 2013 Commercial Credit Exposure [Member] Commercial Real Estate [Member] Substandard [Member] ACQUIRED [Member]	Mar. 31, 2013 Commercial Credit Exposure [Member] Commercial Real Estate [Member] Substandard [Member] ORIGINATED [Member]	Dec. 31, 2012 Commercial Credit Exposure [Member] Commercial Real Estate [Member] Doubtful [Member]	Mar. 31, 2013 Commercial Credit Exposure [Member] Commercial Real Estate [Member] Doubtful [Member] ACQUIRED [Member]	Mar. 31, 2013 Commercial Credit Exposure [Member] Commercial Real Estate [Member] Doubtful [Member] ORIGINATED [Member]	Dec. 31, 2012 Commercial Credit Exposure [Member] Agricultural [Member]	Mar. 31, 2013 Commercial Credit Exposure [Member] Agricultural [Member] ORIGINATED [Member]	Dec. 31, 2012 Commercial Credit Exposure [Member] Agricultural [Member] Pass [Member]	Mar. 31, 2013 Commercial Credit Exposure [Member] Agricultural [Member] Pass [Member] ORIGINATED [Member]	Dec. 31, 2012 Commercial Credit Exposure [Member] Agricultural [Member] Special Mention [Member]	Mar. 31, 2013 Commercial Credit Exposure [Member] Agricultural [Member] Special Mention [Member] ORIGINATED [Member]	Dec. 31, 2012 Commercial Credit Exposure [Member] Agricultural [Member] Substandard [Member]	Mar. 31, 2013 Commercial Credit Exposure [Member] Agricultural [Member] Substandard [Member] ORIGINATED [Member]	Dec. 31, 2012 Commercial Credit Exposure [Member] Agricultural [Member] Doubtful [Member]	Mar. 31, 2013 Commercial Credit Exposure [Member] Agricultural [Member] Doubtful [Member] ORIGINATED [Member]	Dec. 31, 2012 Commercial Credit Exposure [Member] Agricultural Real Estate [Member]	Mar. 31, 2013 Commercial Credit Exposure [Member] Agricultural Real Estate [Member] ORIGINATED [Member]	Dec. 31, 2012 Commercial Credit Exposure [Member] Agricultural Real Estate [Member] Pass [Member]	Mar. 31, 2013 Commercial Credit Exposure [Member] Agricultural Real Estate [Member] Pass [Member] ORIGINATED [Member]	Dec. 31, 2012 Commercial Credit Exposure [Member] Agricultural Real Estate [Member] Special Mention [Member]	Mar. 31, 2013 Commercial Credit Exposure [Member] Agricultural Real Estate [Member] Special Mention [Member] ORIGINATED [Member]	Dec. 31, 2012 Commercial Credit Exposure [Member] Agricultural Real Estate [Member] Substandard [Member]	Mar. 31, 2013 Commercial Credit Exposure [Member] Agricultural Real Estate [Member] Substandard [Member] ORIGINATED [Member]	Dec. 31, 2012 Commercial Credit Exposure [Member] Agricultural Real Estate [Member] Doubtful [Member]	Mar. 31, 2013 Commercial Credit Exposure [Member] Agricultural Real Estate [Member] Doubtful [Member] ORIGINATED [Member]	Dec. 31, 2012 Commercial Credit Exposure [Member] Business Banking [Member]	Mar. 31, 2013 Commercial Credit Exposure [Member] Business Banking [Member] ACQUIRED [Member]	Mar. 31, 2013 Commercial Credit Exposure [Member] Business Banking [Member] ORIGINATED [Member]	Dec. 31, 2012 Commercial Credit Exposure [Member] Business Banking [Member] Non-classified [Member]	Mar. 31, 2013 Commercial Credit Exposure [Member] Business Banking [Member] Non-classified [Member] ACQUIRED [Member]	Mar. 31, 2013 Commercial Credit Exposure [Member] Business Banking [Member] Non-classified [Member] ORIGINATED [Member]	Dec. 31, 2012 Commercial Credit Exposure [Member] Business Banking [Member] Classified [Member]	Mar. 31, 2013 Commercial Credit Exposure [Member] Business Banking [Member] Classified [Member] ACQUIRED [Member]	Mar. 31, 2013 Commercial Credit Exposure [Member] Business Banking [Member] Classified [Member] ORIGINATED [Member]	Mar. 31, 2013 Commercial Credit Exposure [Member] Total Small Business Receivable [Member] ORIGINATED [Member]	Mar. 31, 2013 Commercial Credit Exposure [Member] Total Small Business Receivable [Member] Non-classified [Member] ORIGINATED [Member]	Mar. 31, 2013 Commercial Credit Exposure [Member] Total Small Business Receivable [Member] Classified [Member] ORIGINATED [Member]	Dec. 31, 2012 Consumer Credit Exposure [Member]	Mar. 31, 2013 Consumer Credit Exposure [Member] ACQUIRED [Member]	Mar. 31, 2013 Consumer Credit Exposure [Member] ORIGINATED [Member]	Dec. 31, 2012 Consumer Credit Exposure [Member] Performing [Member]	Mar. 31, 2013 Consumer Credit Exposure [Member] Performing [Member] ACQUIRED [Member]	Mar. 31, 2013 Consumer Credit Exposure [Member] Performing [Member] ORIGINATED [Member]	Dec. 31, 2012 Consumer Credit Exposure [Member] Nonperforming [Member]	Mar. 31, 2013 Consumer Credit Exposure [Member] Nonperforming [Member] ACQUIRED [Member]	Mar. 31, 2013 Consumer Credit Exposure [Member] Nonperforming [Member] ORIGINATED [Member]	Dec. 31, 2012 Consumer Credit Exposure [Member] Indirect [Member]	Mar. 31, 2013 Consumer Credit Exposure [Member] Indirect [Member] ACQUIRED [Member]	Mar. 31, 2013 Consumer Credit Exposure [Member] Indirect [Member] ORIGINATED [Member]	Dec. 31, 2012 Consumer Credit Exposure [Member] Indirect [Member] Performing [Member]	Mar. 31, 2013 Consumer Credit Exposure [Member] Indirect [Member] Performing [Member] ACQUIRED [Member]	Mar. 31, 2013 Consumer Credit Exposure [Member] Indirect [Member] Performing [Member] ORIGINATED [Member]	Dec. 31, 2012 Consumer Credit Exposure [Member] Indirect [Member] Nonperforming [Member]	Mar. 31, 2013 Consumer Credit Exposure [Member] Indirect [Member] Nonperforming [Member] ACQUIRED [Member]	Mar. 31, 2013 Consumer Credit Exposure [Member] Indirect [Member] Nonperforming [Member] ORIGINATED [Member]	Dec. 31, 2012 Consumer Credit Exposure [Member] Home Equity Member]	Mar. 31, 2013 Consumer Credit Exposure [Member] Home Equity Member] ACQUIRED [Member]	Mar. 31, 2013 Consumer Credit Exposure [Member] Home Equity Member] ORIGINATED [Member]	Dec. 31, 2012 Consumer Credit Exposure [Member] Home Equity Member] Performing [Member]	Mar. 31, 2013 Consumer Credit Exposure [Member] Home Equity Member] Performing [Member] ACQUIRED [Member]	Mar. 31, 2013 Consumer Credit Exposure [Member] Home Equity Member] Performing [Member] ORIGINATED [Member]	Dec. 31, 2012 Consumer Credit Exposure [Member] Home Equity Member] Nonperforming [Member]	Mar. 31, 2013 Consumer Credit Exposure [Member] Home Equity Member] Nonperforming [Member] ACQUIRED [Member]	Mar. 31, 2013 Consumer Credit Exposure [Member] Home Equity Member] Nonperforming [Member] ORIGINATED [Member]	Dec. 31, 2012 Consumer Credit Exposure [Member] Direct [Member]	Mar. 31, 2013 Consumer Credit Exposure [Member] Direct [Member] ACQUIRED [Member]	Mar. 31, 2013 Consumer Credit Exposure [Member] Direct [Member] ORIGINATED [Member]	Dec. 31, 2012 Consumer Credit Exposure [Member] Direct [Member] Performing [Member]	Mar. 31, 2013 Consumer Credit Exposure [Member] Direct [Member] Performing [Member] ACQUIRED [Member]	Mar. 31, 2013 Consumer Credit Exposure [Member] Direct [Member] Performing [Member] ORIGINATED [Member]	Dec. 31, 2012 Consumer Credit Exposure [Member] Direct [Member] Nonperforming [Member]	Mar. 31, 2013 Consumer Credit Exposure [Member] Direct [Member] Nonperforming [Member] ACQUIRED [Member]	Mar. 31, 2013 Consumer Credit Exposure [Member] Direct [Member] Nonperforming [Member] ORIGINATED [Member]	Dec. 31, 2012 Residential Mortgage Credit Exposure [Member]	Mar. 31, 2013 Residential Mortgage Credit Exposure [Member] ACQUIRED [Member]	Mar. 31, 2013 Residential Mortgage Credit Exposure [Member] ORIGINATED [Member]	Dec. 31, 2012 Residential Mortgage Credit Exposure [Member] Performing [Member]	Mar. 31, 2013 Residential Mortgage Credit Exposure [Member] Performing [Member] ACQUIRED [Member]	Mar. 31, 2013 Residential Mortgage Credit Exposure [Member] Performing [Member] ORIGINATED [Member]	Dec. 31, 2012 Residential Mortgage Credit Exposure [Member] Nonperforming [Member]	Mar. 31, 2013 Residential Mortgage Credit Exposure [Member] Nonperforming [Member] ACQUIRED [Member]	Mar. 31, 2013 Residential Mortgage Credit Exposure [Member] Nonperforming [Member] ORIGINATED [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	$ 1,637,411	$ 377,820	$ 1,504,252	$ 1,515,732	$ 348,003	$ 1,430,364	$ 50,552	$ 9,381	$ 34,798	$ 68,347	$ 20,436	$ 38,556	$ 2,780	$ 0	$ 534	$ 561,481	$ 133,319	$ 549,494	$ 522,985	$ 122,178	$ 525,022	$ 18,401	$ 3,013	$ 14,810	$ 17,351	$ 8,128	$ 9,159	$ 2,744	$ 0	$ 503	$ 974,795	$ 244,501	$ 859,234	$ 901,928	$ 225,825	$ 819,736	$ 32,135	$ 6,368	$ 19,972	$ 40,732	$ 12,308	$ 19,526	$ 0	$ 0	$ 0	$ 63,758	$ 61,185	$ 57,347	$ 55,091	$ 13	$ 13	$ 6,362	$ 6,050	$ 36	$ 31	$ 37,377	$ 34,339	$ 33,472	$ 30,515	$ 3	$ 3	$ 3,902	$ 3,821	$ 0	$ 0	$ 365,960	$ 88,853	$ 336,029	$ 342,528	$ 83,990	$ 315,645	$ 23,432	$ 4,863	$ 20,384	$ 336,029	$ 315,645	$ 20,384	$ 1,623,138	$ 294,780	$ 1,596,374	$ 1,612,098	$ 293,944	$ 1,585,633	$ 11,040	$ 836	$ 10,741	$ 980,997	$ 187,737	$ 994,138	$ 978,235	$ 187,528	$ 991,493	$ 2,762	$ 209	$ 2,645	$ 575,282	$ 97,572	$ 539,937	$ 567,354	$ 97,040	$ 532,163	$ 7,928	$ 532	$ 7,774	$ 66,859	$ 9,471	$ 62,299	$ 66,509	$ 9,376	$ 61,977	$ 350	$ 95	$ 322	$ 651,107	$ 361,680	$ 635,245	$ 641,608	$ 358,967	$ 627,105	$ 9,499	$ 2,713	$ 8,140