Allowance for Loan and Lease Losses (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of year				$ 36,808				$ 42,693	$ 36,808	$ 42,693	$ 41,848
Provision for loan and lease losses	3,350	(502)	3,000	2,354	7,784	7,727	3,845	10,009	8,202	29,365	32,508
Recoveries									8,209	4,730	2,387
Charge-offs									(14,504)	(39,980)	(34,050)
Balance at end of year	38,715				36,808				38,715	36,808	42,693
Agricultural Portfolio Segment
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of year				1,763				2,147	1,763	2,147
Provision for loan and lease losses									295	(250)
Recoveries									81	33
Charge-offs									(1)	(167)
Balance at end of year	2,138				1,763				2,138	1,763
Residential Portfolio Segment
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of year				3,001				2,381	3,001	2,381
Provision for loan and lease losses									1,366	2,452
Recoveries									164	46
Charge-offs									(988)	(1,878)
Balance at end of year	3,543				3,001				3,543	3,001
Consumer Portfolio Segment
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of year				6,874				6,315	6,874	6,315
Provision for loan and lease losses									4,313	5,288
Recoveries									804	732
Charge-offs									(4,818)	(5,461)
Balance at end of year	7,173				6,874				7,173	6,874
Finance Leases Portfolio Segment
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of year				2				9	2	9
Provision for loan and lease losses									(2)	(7)
Recoveries									0	0
Charge-offs									0	0
Balance at end of year	0				2				0	2
Unallocated Financing Receivables
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of year				0				1,000	0	1,000
Provision for loan and lease losses									0	(1,000)
Recoveries									0	0
Charge-offs									0	0
Balance at end of year	0				0				0	0
Commercial | Commercial Portfolio Segment
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of year				10,547				10,525	10,547	10,525
Provision for loan and lease losses									674	1,941
Recoveries									1,966	1,051
Charge-offs									(1,799)	(2,970)
Balance at end of year	11,388				10,547				11,388	10,547
Commercial Real Estate | Commercial Portfolio Segment
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of year				14,621				20,316	14,621	20,316
Provision for loan and lease losses									1,556	20,941
Recoveries									5,194	2,868
Charge-offs									(6,898)	(29,504)
Balance at end of year	$ 14,473				$ 14,621				$ 14,473	$ 14,621