Allowance for Loan and Lease Losses (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance	$ 38,715	$ 36,808
Charge-offs	(3,064)	(1,608)
Recoveries	1,240	1,808
Provision	637	2,354
Ending Balance	37,528	39,362
Agricultural Portfolio Segment
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance	2,138	1,763
Charge-offs	(23)	0
Recoveries	12	78
Provision	68	6
Ending Balance	2,195	1,847
Residential Portfolio Segment
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance	3,543	3,001
Charge-offs	(265)	(63)
Recoveries	7	33
Provision	(19)	569
Ending Balance	3,266	3,540
Consumer Portfolio Segment
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance	7,173	6,874
Charge-offs	(995)	(757)
Recoveries	254	234
Provision	1,146	1,204
Ending Balance	7,578	7,555
Finance Leases Portfolio Segment
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance	0	2
Charge-offs	0	0
Recoveries	0	0
Provision	0	(1)
Ending Balance	0	1
Unallocated Financing Receivables
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance	0	0
Charge-offs	0	0
Recoveries	0	0
Provision	0	0
Ending Balance	0	0
Commercial | Commercial Portfolio Segment
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance	11,388	10,547
Charge-offs	(538)	(502)
Recoveries	781	33
Provision	(2,332)	941
Ending Balance	9,299	11,019
Commercial Real Estate | Commercial Portfolio Segment
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance	14,473	14,621
Charge-offs	(1,243)	(286)
Recoveries	186	1,430
Provision	1,774	(365)
Ending Balance	$ 15,190	$ 15,400