Fair Value (Quantitative Information about Level 3 fair value measurements) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2015		Dec. 31, 2014
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Securities available for sale	$ 1,353,537		$ 1,401,868
Corporate Debt Securities
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Securities available for sale	740		0
Recurring Basis | Interest rate lock commitments
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Derivative assets	6,875		2,496
Recurring Basis | Corporate Debt Securities
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Securities available for sale	740		0
Nonrecurring Basis
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Collateral dependent impaired loans	10,863		19,345
Other real estate owned	19,097		19,016
Nonrecurring Basis | Commercial
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Collateral dependent impaired loans	68		1,033
Nonrecurring Basis | Commercial real estate
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Collateral dependent impaired loans	6,285		12,584
Nonrecurring Basis | Agricultural and agricultural real estate
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Collateral dependent impaired loans	276		552
Nonrecurring Basis | Residential real estate
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Collateral dependent impaired loans	2,474		3,173
Nonrecurring Basis | Consumer
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Collateral dependent impaired loans	1,760		2,003
Level 3
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Securities available for sale	5,823		4,947
Derivative assets	0		0
Level 3 | Interest rate lock commitments
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Derivative assets	6,875		2,496
Level 3 | Recurring Basis | Interest rate lock commitments
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Derivative assets	6,875	[1]	2,496
Closing ratio	83.00%		84.00%
Level 3 | Recurring Basis | Z-Tranche Securities
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Securities available for sale	5,083		4,947
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%		15.60%
Actual deferrals	6.25%		7.20%
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%		30.60%
Actual deferrals	22.35%		17.30%
Level 3 | Recurring Basis | Z-Tranche Securities | Weighted Average
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Actual defaults	15.52%		24.50%
Actual deferrals	11.32%		12.90%
Level 3 | Recurring Basis | Z-Tranche Securities | Interest rate lock commitments
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Derivative assets			2,496	[2]
Level 3 | Recurring Basis | Corporate Debt Securities
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Securities available for sale	740	[3]	0	[3]
Level 3 | Nonrecurring Basis
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Collateral dependent impaired loans	10,863		19,345
Other real estate owned	19,097	[4]	19,016	[4]
Level 3 | Nonrecurring Basis | Commercial
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Collateral dependent impaired loans	68	[4]	1,033	[4]
Level 3 | Nonrecurring Basis | Commercial real estate
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Collateral dependent impaired loans	6,285	[4]	12,584	[4]
Level 3 | Nonrecurring Basis | Agricultural and agricultural real estate
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Collateral dependent impaired loans	276	[4]	552	[4]
Level 3 | Nonrecurring Basis | Residential real estate
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Collateral dependent impaired loans	2,474	[4]	3,173	[4]
Level 3 | Nonrecurring Basis | Consumer
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Collateral dependent impaired loans	$ 1,760	[4]	$ 2,003	[4]

[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 March 31, 2015 was 83%.

[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, 2014 was 84%.

[3] The unobservable input is the bank analysis market using Moody's Global Bank Rating Methodology. The analysis takes into consideration various performance metrics as well as yield on the debt securities and credit risk analysis.

[4] 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.