Fair Value (Estimated Fair Value Financial Instruments (Including Carrying Amounts)) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Financial assets:
Available for sale	$ 1,845,864	$ 1,578,434
Held to maturity	274,799	294,513
Quoted Prices in Active Markets for Identical Assets (Level 1)
Financial assets:
Cash and cash equivalents	158,724	258,799
Time deposits in other financial institutions	2,105	2,355
Available for sale	517	519
Held to maturity	0	0
Other investments	0	0
Loans held for sale	0	0
Loans, net	0	0
Derivatives	0	0
Financial liabilities:
Short term borrowings	0	0
Other borrowings	0	0
Derivatives	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Interest rate lock commitments
Financial assets:
Derivatives	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Forward commitments
Financial assets:
Derivatives	0	0
Financial liabilities:
Derivatives	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Demand deposits
Financial liabilities:
Deposits	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Savings deposits
Financial liabilities:
Deposits	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Time deposits
Financial liabilities:
Deposits	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Commercial | Commercial
Financial assets:
Loans, net	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Commercial | Commercial real estate
Financial assets:
Loans, net	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Agricultural and agricultural real estate
Financial assets:
Loans, net	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Residential real estate
Financial assets:
Loans, net	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Consumer
Financial assets:
Loans, net	0	0
Significant Other Observable Inputs (Level 2)
Financial assets:
Cash and cash equivalents	0	0
Time deposits in other financial institutions	0	0
Available for sale	1,843,123	1,575,030
Held to maturity	274,799	294,513
Other investments	21,365	21,208
Loans held for sale	61,261	74,783
Loans, net	5,259,690	4,939,712
Derivatives	3,222	2,237
Financial liabilities:
Short term borrowings	306,459	293,898
Other borrowings	288,534	281,271
Derivatives	7,027	8,401
Significant Other Observable Inputs (Level 2) | Interest rate lock commitments
Financial assets:
Derivatives	0	0
Significant Other Observable Inputs (Level 2) | Forward commitments
Financial assets:
Derivatives	2,546	523
Financial liabilities:
Derivatives	266	315
Significant Other Observable Inputs (Level 2) | Demand deposits
Financial liabilities:
Deposits	2,202,036	1,914,141
Significant Other Observable Inputs (Level 2) | Savings deposits
Financial liabilities:
Deposits	3,788,089	3,367,479
Significant Other Observable Inputs (Level 2) | Time deposits
Financial liabilities:
Deposits	857,286	1,124,203
Significant Other Observable Inputs (Level 2) | Commercial | Commercial
Financial assets:
Loans, net	1,257,071	1,256,758
Significant Other Observable Inputs (Level 2) | Commercial | Commercial real estate
Financial assets:
Loans, net	2,503,832	2,303,194
Significant Other Observable Inputs (Level 2) | Agricultural and agricultural real estate
Financial assets:
Loans, net	485,046	469,485
Significant Other Observable Inputs (Level 2) | Residential real estate
Financial assets:
Loans, net	600,668	529,601
Significant Other Observable Inputs (Level 2) | Consumer
Financial assets:
Loans, net	413,073	380,674
Significant Unobservable Inputs (Level 3)
Financial assets:
Cash and cash equivalents	0	0
Time deposits in other financial institutions	0	0
Available for sale	2,224	2,885
Held to maturity	0	0
Other investments	195	235
Loans held for sale	0	0
Loans, net	11,422	6,354
Derivatives	0	0
Financial liabilities:
Short term borrowings	0	0
Other borrowings	0	0
Derivatives	0	0
Significant Unobservable Inputs (Level 3) | Interest rate lock commitments
Financial assets:
Derivatives	2,790	3,168
Significant Unobservable Inputs (Level 3) | Forward commitments
Financial assets:
Derivatives	0	0
Financial liabilities:
Derivatives	0	0
Significant Unobservable Inputs (Level 3) | Demand deposits
Financial liabilities:
Deposits	0	0
Significant Unobservable Inputs (Level 3) | Savings deposits
Financial liabilities:
Deposits	0	0
Significant Unobservable Inputs (Level 3) | Time deposits
Financial liabilities:
Deposits	0	0
Significant Unobservable Inputs (Level 3) | Commercial | Commercial
Financial assets:
Loans, net	1,683	597
Significant Unobservable Inputs (Level 3) | Commercial | Commercial real estate
Financial assets:
Loans, net	3,026	1,522
Significant Unobservable Inputs (Level 3) | Agricultural and agricultural real estate
Financial assets:
Loans, net	1,955	0
Significant Unobservable Inputs (Level 3) | Residential real estate
Financial assets:
Loans, net	3,565	2,330
Significant Unobservable Inputs (Level 3) | Consumer
Financial assets:
Loans, net	1,193	1,905
Carrying Amount
Financial assets:
Cash and cash equivalents	158,724	258,799
Time deposits in other financial institutions	2,105	2,355
Available for sale	1,845,864	1,578,434
Held to maturity	263,662	279,117
Other investments	21,560	21,443
Loans held for sale	61,261	74,783
Loans, net	5,297,395	4,952,801
Derivatives	3,222	2,237
Financial liabilities:
Short term borrowings	306,459	293,898
Other borrowings	288,534	263,214
Derivatives	7,027	8,401
Carrying Amount | Interest rate lock commitments
Financial assets:
Derivatives	2,790	3,168
Carrying Amount | Forward commitments
Financial assets:
Derivatives	2,546	523
Financial liabilities:
Derivatives	266	315
Carrying Amount | Demand deposits
Financial liabilities:
Deposits	2,202,036	1,914,141
Carrying Amount | Savings deposits
Financial liabilities:
Deposits	3,788,089	3,367,479
Carrying Amount | Time deposits
Financial liabilities:
Deposits	857,286	1,124,203
Carrying Amount | Commercial | Commercial
Financial assets:
Loans, net	1,272,089	1,262,612
Carrying Amount | Commercial | Commercial real estate
Financial assets:
Loans, net	2,513,446	2,305,908
Carrying Amount | Agricultural and agricultural real estate
Financial assets:
Loans, net	485,820	468,533
Carrying Amount | Residential real estate
Financial assets:
Loans, net	614,207	536,190
Carrying Amount | Consumer
Financial assets:
Loans, net	411,833	379,558
Estimated Fair Value
Financial assets:
Cash and cash equivalents	158,724	258,799
Time deposits in other financial institutions	2,105	2,355
Available for sale	1,845,864	1,578,434
Held to maturity	274,799	294,513
Other investments	21,560	21,443
Loans held for sale	61,261	74,783
Loans, net	5,271,112	4,946,066
Derivatives	3,222	2,237
Financial liabilities:
Short term borrowings	306,459	293,898
Other borrowings	288,534	281,271
Derivatives	7,027	8,401
Estimated Fair Value | Interest rate lock commitments
Financial assets:
Derivatives	2,790	3,168
Estimated Fair Value | Forward commitments
Financial assets:
Derivatives	2,546	523
Financial liabilities:
Derivatives	266	315
Estimated Fair Value | Demand deposits
Financial liabilities:
Deposits	2,202,036	1,914,141
Estimated Fair Value | Savings deposits
Financial liabilities:
Deposits	3,788,089	3,367,479
Estimated Fair Value | Time deposits
Financial liabilities:
Deposits	857,286	1,124,203
Estimated Fair Value | Commercial | Commercial
Financial assets:
Loans, net	1,258,754	1,257,355
Estimated Fair Value | Commercial | Commercial real estate
Financial assets:
Loans, net	2,506,858	2,304,716
Estimated Fair Value | Agricultural and agricultural real estate
Financial assets:
Loans, net	487,001	469,485
Estimated Fair Value | Residential real estate
Financial assets:
Loans, net	604,233	531,931
Estimated Fair Value | Consumer
Financial assets:
Loans, net	$ 414,266	$ 382,579