Fair Value (Quantitative Information about Level 3 fair value measurements) (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2016	Dec. 31, 2015
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Securities available for sale	$ 1,566,592	$ 1,578,434
Premises, furniture and equipment held for sale	$ 3,889	$ 3,889
Commercial servicing rights | Minimum
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Pretax discount rate	11.68%	12.35%
Commercial servicing rights | Maximum
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Pretax discount rate	12.68%	13.49%
Corporate debt securities
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Securities available for sale	$ 830	$ 846
Level 3
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Securities available for sale	2,062	2,885
Derivative assets	0	0
Other real estate owned	11,003	11,524
Level 3 | Commercial
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Collateral dependent impaired loans	1,333	597
Level 3 | Commercial real estate
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Collateral dependent impaired loans	14,113	1,522
Level 3 | Agricultural and agricultural real estate
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Collateral dependent impaired loans	105	0
Level 3 | Residential real estate
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Collateral dependent impaired loans	3,508	2,330
Level 3 | Consumer
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Collateral dependent impaired loans	1,845	1,905
Level 3 | Commercial servicing rights
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Commercial servicing rights	1,258	0
Level 3 | Premises, furniture and equipment held for sale
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Premises, furniture and equipment held for sale	3,889	3,889
Level 3 | Interest rate lock commitments
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Derivative assets	$ 6,864	$ 3,168
Closing ratio	87.00%	86.00%
Level 3 | Z-TRANCHE Securities
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Securities available for sale	$ 1,732	$ 2,039
Level 3 | Z-TRANCHE Securities | Minimum
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Pretax discount rate	7.50%	7.50%
Actual defaults (as a percent)	19.85%	22.20%
Actual deferrals (as a percent)	9.57%	10.75%
Level 3 | Z-TRANCHE Securities | Maximum
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Pretax discount rate	9.50%	9.50%
Actual defaults (as a percent)	34.02%	33.55%
Actual deferrals (as a percent)	22.12%	21.82%
Level 3 | Z-TRANCHE Securities | Weighted Average
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Actual defaults (as a percent)	30.17%	30.60%
Actual deferrals (as a percent)	13.34%	13.36%
Level 3 | Corporate debt securities
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Securities available for sale	$ 330	$ 846