Fair Value (Estimated fair value financial instruments (incl. carrying amounts)) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Financial assets:
Securities available for sale	$ 1,353,537us-gaap_AvailableForSaleSecurities	$ 1,401,868us-gaap_AvailableForSaleSecurities
Held to maturity securities	297,660	296,768
Quoted Prices in Active Markets for Identical Assets (Level 1)
Financial assets:
Cash and cash equivalents	111,732	73,871
Time deposits in other financial institutions	2,605	2,605
Securities available for sale	530	2,529
Held to maturity securities	0	0
Other investments	0	0
Loans held for sale	0	0
Loans, net	0	0
Derivative assets	0	0
Financial liabilities:
Short term borrowings	0	0
Other borrowings	0	0
Derivative liabilities	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) \| Interest rate lock commitments
Financial assets:
Derivative assets	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Forward commitments
Financial assets:
Derivative assets	0	0
Financial liabilities:
Derivative liabilities	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Commercial
Financial assets:
Loans, net	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) \| 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
Securities available for sale	1,347,184	1,394,392
Held to maturity securities	297,660	296,768
Other investments	18,062	20,263
Loans held for sale	105,670	70,514
Loans, net	4,183,297	3,814,536
Derivative assets	0	0
Financial liabilities:
Short term borrowings	259,335	330,264
Other borrowings	364,534	401,978
Derivative liabilities	4,536	3,646
Significant Other Observable Inputs (Level 2) \| Demand Deposits
Financial liabilities:
Deposits	1,515,004	1,295,193
Significant Other Observable Inputs (Level 2) \| Savings Deposits
Financial liabilities:
Deposits	2,863,744	2,687,493
Significant Other Observable Inputs (Level 2) \| Time Deposits
Financial liabilities:
Deposits	887,650	785,336
Significant Other Observable Inputs (Level 2) \| Interest rate lock commitments
Financial assets:
Derivative assets	0	0
Significant Other Observable Inputs (Level 2) \| Forward commitments
Financial assets:
Derivative assets	404	275
Financial liabilities:
Derivative liabilities	1,873	1,619
Significant Other Observable Inputs (Level 2) \| Commercial
Financial assets:
Loans, net	1,095,443	1,008,769
Significant Other Observable Inputs (Level 2) \| Commercial real estate
Financial assets:
Loans, net	1,928,350	1,687,138
Significant Other Observable Inputs (Level 2) \| Agricultural and agricultural real estate
Financial assets:
Loans, net	412,348	423,416
Significant Other Observable Inputs (Level 2) \| Residential real estate
Financial assets:
Loans, net	397,923	367,005
Significant Other Observable Inputs (Level 2) \| Consumer
Financial assets:
Loans, net	349,233	328,208
Significant Unobservable Inputs (Level 3)
Financial assets:
Cash and cash equivalents	0	0
Time deposits in other financial institutions	0	0
Securities available for sale	5,823	4,947
Held to maturity securities	0	0
Other investments	235	235
Loans held for sale	0	0
Loans, net	10,863	19,345
Derivative assets	0	0
Financial liabilities:
Short term borrowings	0	0
Other borrowings	0	0
Derivative liabilities	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) \| Interest rate lock commitments
Financial assets:
Derivative assets	6,875	2,496
Significant Unobservable Inputs (Level 3) \| Forward commitments
Financial assets:
Derivative assets	0	0
Financial liabilities:
Derivative liabilities	0	0
Significant Unobservable Inputs (Level 3) \| Commercial
Financial assets:
Loans, net	68	1,033
Significant Unobservable Inputs (Level 3) \| Commercial real estate
Financial assets:
Loans, net	6,285	12,584
Significant Unobservable Inputs (Level 3) \| Agricultural and agricultural real estate
Financial assets:
Loans, net	276	552
Significant Unobservable Inputs (Level 3) \| Residential real estate
Financial assets:
Loans, net	2,474	3,173
Significant Unobservable Inputs (Level 3) \| Consumer
Financial assets:
Loans, net	1,760	2,003
Carrying Amount
Financial assets:
Cash and cash equivalents	111,732	73,871
Time deposits in other financial institutions	2,605	2,605
Securities available for sale	1,353,537	1,401,868
Held to maturity securities	284,030	284,587
Other investments	18,297	20,498
Loans held for sale	105,670	70,514
Loans, net	4,201,835	3,836,554
Derivative assets	0	0
Financial liabilities:
Short term borrowings	259,335	330,264
Other borrowings	361,300	396,255
Derivative liabilities	4,536	3,646
Carrying Amount \| Demand Deposits
Financial liabilities:
Deposits	1,515,004	1,295,193
Carrying Amount \| Savings Deposits
Financial liabilities:
Deposits	2,863,744	2,687,493
Carrying Amount \| Time Deposits
Financial liabilities:
Deposits	887,650	785,336
Carrying Amount \| Interest rate lock commitments
Financial assets:
Derivative assets	6,875	2,496
Carrying Amount \| Forward commitments
Financial assets:
Derivative assets	404	275
Financial liabilities:
Derivative liabilities	1,873	1,619
Carrying Amount \| Commercial
Financial assets:
Loans, net	1,122,604	1,024,065
Carrying Amount \| Commercial real estate
Financial assets:
Loans, net	1,915,520	1,690,899
Carrying Amount \| Agricultural and agricultural real estate
Financial assets:
Loans, net	409,561	420,623
Carrying Amount \| Residential real estate
Financial assets:
Loans, net	408,808	377,094
Carrying Amount \| Consumer
Financial assets:
Loans, net	345,342	323,873
Estimated Fair Value
Financial assets:
Cash and cash equivalents	111,732	73,871
Time deposits in other financial institutions	2,605	2,605
Securities available for sale	1,353,537	1,401,868
Held to maturity securities	297,660	296,768
Other investments	18,297	20,498
Loans held for sale	105,670	70,514
Loans, net	4,194,160	3,833,881
Derivative assets	0	0
Financial liabilities:
Short term borrowings	259,335	330,264
Other borrowings	364,534	401,978
Derivative liabilities	4,536	3,646
Estimated Fair Value \| Demand Deposits
Financial liabilities:
Deposits	1,515,004	1,295,193
Estimated Fair Value \| Savings Deposits
Financial liabilities:
Deposits	2,863,744	2,687,493
Estimated Fair Value \| Time Deposits
Financial liabilities:
Deposits	887,650	785,336
Estimated Fair Value \| Interest rate lock commitments
Financial assets:
Derivative assets	6,875	2,496
Estimated Fair Value \| Forward commitments
Financial assets:
Derivative assets	404	275
Financial liabilities:
Derivative liabilities	1,873	1,619
Estimated Fair Value \| Commercial
Financial assets:
Loans, net	1,095,511	1,009,802
Estimated Fair Value \| Commercial real estate
Financial assets:
Loans, net	1,934,635	1,699,722
Estimated Fair Value \| Agricultural and agricultural real estate
Financial assets:
Loans, net	412,624	423,968
Estimated Fair Value \| Residential real estate
Financial assets:
Loans, net	400,397	370,178
Estimated Fair Value \| Consumer
Financial assets:
Loans, net	$ 350,993	$ 330,211

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Fair value portion of deposit liabilities held by the entity, including, but not limited to, foreign and domestic, interest and noninterest bearing, demand deposits, saving deposits, negotiable orders of withdrawal (NOW) and time deposits.

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Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

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Fair value of investments in debt securities classified as held-to-maturity.

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Fair value portion of loans held-for-sale including, but not limited to, mortgage loans and finance receivables.

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Other investments not otherwise specified in the taxonomy.

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