Fair Value (Quantitative Information about Level 3 fair value measurements) (Details) - USD ($) $ in Thousands		9 Months Ended		12 Months Ended
		Sep. 30, 2015		Dec. 31, 2014
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Securities available for sale		$ 1,261,687		$ 1,401,868
Premises, furniture and equipment held for sale		3,440		0
Corporate debt securities
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Securities available for sale		580		0
Recurring Basis | Interest rate lock commitments
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Derivative assets		4,903		2,496
Recurring Basis | Corporate debt securities
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Securities available for sale		580		0
Nonrecurring Basis
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Collateral dependent impaired loans		9,489		19,345
Other real estate owned		17,041		19,016
Nonrecurring Basis | Commercial
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Collateral dependent impaired loans		767		1,033
Nonrecurring Basis | Commercial real estate
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Collateral dependent impaired loans		4,277		12,584
Nonrecurring Basis | Agricultural and agricultural real estate
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Collateral dependent impaired loans		0		552
Nonrecurring Basis | Residential real estate
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Collateral dependent impaired loans		2,475		3,173
Nonrecurring Basis | Consumer
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Collateral dependent impaired loans		1,970		2,003
Nonrecurring Basis | Premises, furniture and equipment held for sale
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Premises, furniture and equipment held for sale		3,440		0
Level 3
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Securities available for sale		6,620		4,947
Level 3 | Interest rate lock commitments
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Derivative assets		4,903		2,496
Level 3 | Recurring Basis | Premises, furniture and equipment held for sale
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Premises, furniture and equipment held for sale	[1]	3,440		0
Level 3 | Recurring Basis | Interest rate lock commitments
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Derivative assets		$ 4,903	[1]	$ 2,496	[2]
Closing ratio		86.00%		84.00%
Level 3 | Recurring Basis | Z-TRANCHE Securities
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Securities available for sale		$ 6,040		$ 4,947
Level 3 | Recurring Basis | Z-TRANCHE Securities | Minimum
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Pretax discount rate		7.00%		7.00%
Actual defaults (as a percent)		17.28%		15.60%
Actual deferrals (as a percent)		4.91%		7.20%
Level 3 | Recurring Basis | Z-TRANCHE Securities | Maximum
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Pretax discount rate		9.50%		9.00%
Actual defaults (as a percent)		32.60%		30.60%
Actual deferrals (as a percent)		21.20%		17.30%
Level 3 | Recurring Basis | Z-TRANCHE Securities | Weighted Average
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Actual defaults (as a percent)		26.32%		24.50%
Actual deferrals (as a percent)		16.30%		12.90%
Level 3 | Recurring Basis | Corporate debt securities
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Securities available for sale	[3]	$ 580		$ 0
Level 3 | Nonrecurring Basis
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Collateral dependent impaired loans		9,489		19,345
Other real estate owned	[4]	17,041		19,016
Level 3 | Nonrecurring Basis | Commercial
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Collateral dependent impaired loans	[4]	767		1,033
Level 3 | Nonrecurring Basis | Commercial real estate
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Collateral dependent impaired loans	[4]	4,277		12,584
Level 3 | Nonrecurring Basis | Agricultural and agricultural real estate
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Collateral dependent impaired loans	[4]	0		552
Level 3 | Nonrecurring Basis | Residential real estate
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Collateral dependent impaired loans	[4]	2,475		3,173
Level 3 | Nonrecurring Basis | Consumer
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Collateral dependent impaired loans	[4]	1,970		2,003
Level 3 | Nonrecurring Basis | Premises, furniture and equipment held for sale
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Premises, furniture and equipment held for sale		$ 3,440		$ 0

[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, 2015, was 86%.

[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.