Fair Value (Quantitative Information about Level 3 fair value measurements) (Details) (USD $) In Thousands, unless otherwise specified	9 Months Ended		12 Months Ended
	Sep. 30, 2014		Dec. 31, 2013
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Securities available for sale	$ 1,369,703		$ 1,633,902
Recurring Basis | Interest rate lock commitments
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Derivative assets	3,291		1,809
Nonrecurring Basis
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Collateral dependent impaired loans	14,976		33,199
Other real estate owned	20,475		29,852
Nonrecurring Basis | Commercial
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Collateral dependent impaired loans	1,545		7,229
Nonrecurring Basis | Commercial real estate
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Collateral dependent impaired loans	7,058		7,749
Nonrecurring Basis | Agricultural and agricultural real estate
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Collateral dependent impaired loans	827		13,062
Nonrecurring Basis | Residential real estate
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Collateral dependent impaired loans	2,503		3,396
Nonrecurring Basis | Consumer
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Collateral dependent impaired loans	3,043		1,763
Level 3
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Securities available for sale	4,848		3,298
Derivative assets	0		0
Level 3 | Interest rate lock commitments
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Derivative assets	3,291		1,809
Level 3 | Recurring Basis | Interest rate lock commitments
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Derivative assets	3,291	[1]	1,809
Closing ratio	84.00%		87.00%
Level 3 | Recurring Basis | Z-Tranche Securities
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Securities available for sale	4,848		3,298
Level 3 | Recurring Basis | Z-Tranche Securities | Minimum
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Pretax discount rate	6.50%		7.00%
Actual defaults	12.71%		12.50%
Actual deferrals	6.25%		6.10%
Level 3 | Recurring Basis | Z-Tranche Securities | Maximum
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Pretax discount rate	8.00%		9.00%
Actual defaults	20.14%		28.20%
Actual deferrals	22.35%		16.00%
Level 3 | Recurring Basis | Z-Tranche Securities | Weighted Average
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Actual defaults	15.52%		20.80%
Actual deferrals	11.32%		11.10%
Level 3 | Recurring Basis | Z-Tranche Securities | Interest rate lock commitments
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Derivative assets			1,809	[2]
Level 3 | Nonrecurring Basis
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Collateral dependent impaired loans	14,976		33,199
Other real estate owned	20,475	[3]	29,852	[3]
Level 3 | Nonrecurring Basis | Commercial
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Collateral dependent impaired loans	1,545	[3]	7,229	[3]
Level 3 | Nonrecurring Basis | Commercial real estate
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Collateral dependent impaired loans	7,058	[3]	7,749	[3]
Level 3 | Nonrecurring Basis | Agricultural and agricultural real estate
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Collateral dependent impaired loans	827	[3]	13,062	[3]
Level 3 | Nonrecurring Basis | Residential real estate
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Collateral dependent impaired loans	2,503	[3]	3,396	[3]
Level 3 | Nonrecurring Basis | Consumer
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Collateral dependent impaired loans	$ 3,043	[3]	$ 1,763	[3]

[1] The significant unobservable input used in the fair value measurement is the closing ratio, which represents the percentage of loans currently in a lock position which management estimates will ultimately close. The closing ratio calculation takes into consideration historical data and loan-level data; therefore providing a range would not be meaningful. The weighted average closing ratio at September 30, 2014 was 84%.

[2] The significant unobservable input used in the fair value measurement is the closing ratio, which represents the percentage of loans currently in a lock position which management estimates will ultimately close. The closing ratio calculation takes into consideration historical data and loan-level data; therefore providing a range would not be meaningful. The weighted average closing ratio at December 31, 2013 was 87%.

[3] 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.