Fair Value (Fair value measurement non-recurring) (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013		Dec. 31, 2012
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held for sale	$ 0		$ 0
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held for sale	88,541		96,165
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held for sale	0		0
Nonrecurring Basis | Total Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Collateral dependent impaired loans	39,740		78,952
Other real estate owned	34,763		35,822
Loans held for sale	88,541
Mortgage servicing rights			15,956
Nonrecurring Basis | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Collateral dependent impaired loans	0		0
Other real estate owned	0		0
Loans held for sale	0
Mortgage servicing rights			0
Nonrecurring Basis | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Collateral dependent impaired loans	0		0
Other real estate owned	0		0
Loans held for sale	88,541
Mortgage servicing rights			0
Nonrecurring Basis | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Collateral dependent impaired loans	39,740		78,952
Other real estate owned	34,763	[1]	35,822	[1]
Loans held for sale	0
Mortgage servicing rights			15,956
Nonrecurring Basis | Losses
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Collateral dependent impaired loans	1,352		14,504
Other real estate owned	2,102		6,953
Loans held for sale	371
Mortgage servicing rights			477
Agricultural Portfolio Segment | Nonrecurring Basis | Total Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Collateral dependent impaired loans	15,115		16,019
Agricultural Portfolio Segment | Nonrecurring Basis | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Collateral dependent impaired loans	0		0
Agricultural Portfolio Segment | Nonrecurring Basis | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Collateral dependent impaired loans	0		0
Agricultural Portfolio Segment | Nonrecurring Basis | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Collateral dependent impaired loans	15,115	[1]	16,019	[1]
Agricultural Portfolio Segment | Nonrecurring Basis | Losses
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Collateral dependent impaired loans	0		1
Residential Portfolio Segment | Nonrecurring Basis | Total Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Collateral dependent impaired loans	3,775		6,660
Residential Portfolio Segment | Nonrecurring Basis | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Collateral dependent impaired loans	0		0
Residential Portfolio Segment | Nonrecurring Basis | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Collateral dependent impaired loans	0		0
Residential Portfolio Segment | Nonrecurring Basis | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Collateral dependent impaired loans	3,775	[1]	6,660	[1]
Residential Portfolio Segment | Nonrecurring Basis | Losses
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Collateral dependent impaired loans	252		988
Consumer Portfolio Segment | Nonrecurring Basis | Total Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Collateral dependent impaired loans	1,558		4,121
Consumer Portfolio Segment | Nonrecurring Basis | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Collateral dependent impaired loans	0		0
Consumer Portfolio Segment | Nonrecurring Basis | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Collateral dependent impaired loans	0		0
Consumer Portfolio Segment | Nonrecurring Basis | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Collateral dependent impaired loans	1,558	[1]	4,121	[1]
Consumer Portfolio Segment | Nonrecurring Basis | Losses
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Collateral dependent impaired loans	31		4,818
Commercial | Commercial Portfolio Segment | Nonrecurring Basis | Total Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Collateral dependent impaired loans	1,550		7,681
Commercial | Commercial Portfolio Segment | Nonrecurring Basis | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Collateral dependent impaired loans	0		0
Commercial | Commercial Portfolio Segment | Nonrecurring Basis | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Collateral dependent impaired loans	0		0
Commercial | Commercial Portfolio Segment | Nonrecurring Basis | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Collateral dependent impaired loans	1,550	[1]	7,681	[1]
Commercial | Commercial Portfolio Segment | Nonrecurring Basis | Losses
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Collateral dependent impaired loans	472		1,799
Commercial Real Estate | Commercial Portfolio Segment | Nonrecurring Basis | Total Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Collateral dependent impaired loans	17,742		44,471
Commercial Real Estate | Commercial Portfolio Segment | Nonrecurring Basis | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Collateral dependent impaired loans	0		0
Commercial Real Estate | Commercial Portfolio Segment | Nonrecurring Basis | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Collateral dependent impaired loans	0		0
Commercial Real Estate | Commercial Portfolio Segment | Nonrecurring Basis | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Collateral dependent impaired loans	17,742	[1]	44,471	[1]
Commercial Real Estate | Commercial Portfolio Segment | Nonrecurring Basis | Losses
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Collateral dependent impaired loans	$ 597		$ 6,898

[1] Not Meaningful. Third party appraisals are obtained as to the value of the underlying asset, but disclosure of this information would not provide meaningful information, as the range will vary widely from loan to loan. Types of discounts considered included age of the appraisal, local market conditions, current condition of the property, and estimated sales costs. These discounts will also vary from loan to loan, thus providing range would not be meaningful.