Allowance for Loan and Lease Losses and Credit Quality of Loans and Leases Credit Quality of Loans and Leases (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010
Financing Receivable, Recorded Investment, Aging [Abstract]
31 - 60 Days Past Due Accruing	$ 25,351	$ 23,116
61 - 90 Days Past Due Accruing	5,278	5,563
Greater Than 91 Days Past Due Accruing	3,190	2,325
Total Past Due Accruing	33,819	31,004
Non-Accrual	38,290	42,467
Current	3,728,094	3,536,535
Loans and leases	3,800,203	3,610,006
Home Equity Loan amount, Percentage of Equity in Home, Maximum (in hundredths)	85.00%
Principal repayment terms on direct financing, minimum (in years)	1Y
Principal repayment terms on direct financing, maximum (in years)	10Y
Residential Real Estate Loan amount, percentage of appraised value or purchase price of the property, minimum (in hundredths)	85.00%
Residential Real Estate Loan amount, percentage of appraised value or purchase price of the property, maximum (in hundredths)	95.00%
Commercial Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Loans and leases	1,702,577	1,580,371
Commercial Portfolio Segment [Member] | Commercial Financing Receivable [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
31 - 60 Days Past Due Accruing	663	136
61 - 90 Days Past Due Accruing	50	55
Greater Than 91 Days Past Due Accruing	0	94
Total Past Due Accruing	713	285
Non-Accrual	1,699	5,837
Current	508,662	461,633
Loans and leases	511,074	467,755
Commercial Portfolio Segment [Member] | Commercial Real Estate Other Receivable [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
31 - 60 Days Past Due Accruing	1,942	1,263
61 - 90 Days Past Due Accruing	0	0
Greater Than 91 Days Past Due Accruing	0	0
Total Past Due Accruing	1,942	1,263
Non-Accrual	4,868	5,687
Current	828,089	730,285
Loans and leases	834,899	737,235
Commercial Portfolio Segment [Member] | Agricultural Financing Receivable [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
31 - 60 Days Past Due Accruing	77	63
61 - 90 Days Past Due Accruing	13	92
Greater Than 91 Days Past Due Accruing	0	0
Total Past Due Accruing	90	155
Non-Accrual	3,307	4,065
Current	63,140	63,336
Loans and leases	66,537	67,556
Commercial Portfolio Segment [Member] | Agricultural Real Estate Financing Receivable [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
31 - 60 Days Past Due Accruing	0	108
61 - 90 Days Past Due Accruing	0	0
Greater Than 91 Days Past Due Accruing	50	0
Total Past Due Accruing	50	108
Non-Accrual	2,067	2,429
Current	31,809	33,400
Loans and leases	33,926	35,937
Commercial Portfolio Segment [Member] | Small Business Financing Receivable [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
31 - 60 Days Past Due Accruing	1,871	2,570
61 - 90 Days Past Due Accruing	1,024	1,183
Greater Than 91 Days Past Due Accruing	0	0
Total Past Due Accruing	2,895	3,753
Non-Accrual	7,446	7,033
Current	245,800	261,102
Loans and leases	256,141	271,888
Commercial Portfolio Segment [Member] | Total Commercial Loan Financing Receivable [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
31 - 60 Days Past Due Accruing	4,553	4,140
61 - 90 Days Past Due Accruing	1,087	1,330
Greater Than 91 Days Past Due Accruing	50	94
Total Past Due Accruing	5,690	5,564
Non-Accrual	19,387	25,051
Current	1,677,499	1,549,756
Loans and leases	1,702,577	1,580,371
Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Loans and leases	1,516,115	1,481,241
Consumer Portfolio Segment [Member] | Indirect Financing Receivable [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
31 - 60 Days Past Due Accruing	12,141	9,307
61 - 90 Days Past Due Accruing	2,584	2,193
Greater Than 91 Days Past Due Accruing	1,283	862
Total Past Due Accruing	16,008	12,362
Non-Accrual	1,550	1,971
Current	855,545	814,594
Loans and leases	873,103	828,927
Consumer Portfolio Segment [Member] | Home Equity Financing Receivables [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
31 - 60 Days Past Due Accruing	5,823	5,740
61 - 90 Days Past Due Accruing	1,277	1,756
Greater Than 91 Days Past Due Accruing	954	396
Total Past Due Accruing	8,054	7,892
Non-Accrual	7,931	6,395
Current	553,660	561,391
Loans and leases	569,645	575,678
Consumer Portfolio Segment [Member] | Direct Financing Receivable [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
31 - 60 Days Past Due Accruing	831	927
61 - 90 Days Past Due Accruing	191	158
Greater Than 91 Days Past Due Accruing	140	54
Total Past Due Accruing	1,162	1,139
Non-Accrual	378	399
Current	71,827	75,098
Loans and leases	73,367	76,636
Consumer Portfolio Segment [Member] | Total Consumer Loan Financing Receivable [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
31 - 60 Days Past Due Accruing	18,795	15,974
61 - 90 Days Past Due Accruing	4,052	4,107
Greater Than 91 Days Past Due Accruing	2,377	1,312
Total Past Due Accruing	25,224	21,393
Non-Accrual	9,859	8,765
Current	1,481,032	1,451,083
Loans and leases	1,516,115	1,481,241
Residential Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
31 - 60 Days Past Due Accruing	2,003	3,002
61 - 90 Days Past Due Accruing	139	126
Greater Than 91 Days Past Due Accruing	763	919
Total Past Due Accruing	2,905	4,047
Non-Accrual	9,044	8,651
Current	569,562	535,696
Loans and leases	$ 581,511	$ 548,394