Fair Value of Assets and Liabilities (Fair value on recurring basis) (Details 1) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Assets:
Available-for-Sale: Fair Value	$ 2,184,187	$ 2,232,979
Loans Held for Sale	23,548	19,231
Fair Value, Measurements, Recurring
Assets:
Available-for-Sale: Fair Value	2,184,187	2,232,979
Loans Held for Sale	23,548	19,231
Mortgage Servicing Rights	1,404	1,454
Other Assets	31,106	29,230
Derivatives	14,164	10,518
Total Assets Measured at Fair Value on a Recurring Basis	2,254,409	2,293,412
Liabilites:
Derivatives	13,742	9,693
Total Liabilities Measured at Fair Value on a Recurring Basis	13,742	9,693
Fair Value, Measurements, Recurring \| Debt Securities Issued by the U.S. Treasury and Government Agencies
Assets:
Available-for-Sale: Fair Value	438,410	425,930
Fair Value, Measurements, Recurring \| Debt Securities Issued by States and Political Subdivisions
Assets:
Available-for-Sale: Fair Value	612,004	627,019
Fair Value, Measurements, Recurring \| Debt Securities Issued by Corporations
Assets:
Available-for-Sale: Fair Value	251,066	266,111
Fair Value, Measurements, Recurring \| Mortgage-Backed Securities
Assets:
Available-for-Sale: Fair Value	882,707	913,919
Fair Value, Measurements, Recurring \| Residential - Government Agencies
Assets:
Available-for-Sale: Fair Value	222,541	235,360
Fair Value, Measurements, Recurring \| Residential - U.S. Government-Sponsored Enterprises
Assets:
Available-for-Sale: Fair Value	594,095	609,812
Fair Value, Measurements, Recurring \| Commercial - Government Agencies
Assets:
Available-for-Sale: Fair Value	66,071	68,747
Fair Value, Measurements, Recurring \| Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)
Assets:
Available-for-Sale: Fair Value	535	538
Loans Held for Sale	0	0
Mortgage Servicing Rights	0	0
Other Assets	31,106	29,230
Derivatives	0	0
Total Assets Measured at Fair Value on a Recurring Basis	31,641	29,768
Liabilites:
Derivatives	0	0
Total Liabilities Measured at Fair Value on a Recurring Basis	0	0
Fair Value, Measurements, Recurring \| Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1) \| Debt Securities Issued by the U.S. Treasury and Government Agencies
Assets:
Available-for-Sale: Fair Value	535	538
Fair Value, Measurements, Recurring \| Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1) \| Debt Securities Issued by States and Political Subdivisions
Assets:
Available-for-Sale: Fair Value	0	0
Fair Value, Measurements, Recurring \| Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1) \| Debt Securities Issued by Corporations
Assets:
Available-for-Sale: Fair Value	0	0
Fair Value, Measurements, Recurring \| Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1) \| Mortgage-Backed Securities
Assets:
Available-for-Sale: Fair Value	0	0
Fair Value, Measurements, Recurring \| Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1) \| Residential - Government Agencies
Assets:
Available-for-Sale: Fair Value	0	0
Fair Value, Measurements, Recurring \| Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1) \| Residential - U.S. Government-Sponsored Enterprises
Assets:
Available-for-Sale: Fair Value	0	0
Fair Value, Measurements, Recurring \| Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1) \| Commercial - Government Agencies
Assets:
Available-for-Sale: Fair Value	0	0
Fair Value, Measurements, Recurring \| Significant Other Observable Inputs (Level 2)
Assets:
Available-for-Sale: Fair Value	2,183,652	2,232,441
Loans Held for Sale	23,548	19,231
Mortgage Servicing Rights	0	0
Other Assets	0	0
Derivatives	157	146
Total Assets Measured at Fair Value on a Recurring Basis	2,207,357	2,251,818
Liabilites:
Derivatives	282	215
Total Liabilities Measured at Fair Value on a Recurring Basis	282	215
Fair Value, Measurements, Recurring \| Significant Other Observable Inputs (Level 2) \| Debt Securities Issued by the U.S. Treasury and Government Agencies
Assets:
Available-for-Sale: Fair Value	437,875	425,392
Fair Value, Measurements, Recurring \| Significant Other Observable Inputs (Level 2) \| Debt Securities Issued by States and Political Subdivisions
Assets:
Available-for-Sale: Fair Value	612,004	627,019
Fair Value, Measurements, Recurring \| Significant Other Observable Inputs (Level 2) \| Debt Securities Issued by Corporations
Assets:
Available-for-Sale: Fair Value	251,066	266,111
Fair Value, Measurements, Recurring \| Significant Other Observable Inputs (Level 2) \| Mortgage-Backed Securities
Assets:
Available-for-Sale: Fair Value	882,707	913,919
Fair Value, Measurements, Recurring \| Significant Other Observable Inputs (Level 2) \| Residential - Government Agencies
Assets:
Available-for-Sale: Fair Value	222,541	235,360
Fair Value, Measurements, Recurring \| Significant Other Observable Inputs (Level 2) \| Residential - U.S. Government-Sponsored Enterprises
Assets:
Available-for-Sale: Fair Value	594,095	609,812
Fair Value, Measurements, Recurring \| Significant Other Observable Inputs (Level 2) \| Commercial - Government Agencies
Assets:
Available-for-Sale: Fair Value	66,071	68,747
Fair Value, Measurements, Recurring \| Significant Other Unobservable Inputs (Level 3)
Assets:
Available-for-Sale: Fair Value	0	0
Loans Held for Sale	0	0
Mortgage Servicing Rights	1,404	1,454
Other Assets	0	0
Derivatives	14,007	10,372
Total Assets Measured at Fair Value on a Recurring Basis	15,411	11,826
Liabilites:
Derivatives	13,460	9,478
Total Liabilities Measured at Fair Value on a Recurring Basis	13,460	9,478
Fair Value, Measurements, Recurring \| Significant Other Unobservable Inputs (Level 3) \| Debt Securities Issued by the U.S. Treasury and Government Agencies
Assets:
Available-for-Sale: Fair Value	0	0
Fair Value, Measurements, Recurring \| Significant Other Unobservable Inputs (Level 3) \| Debt Securities Issued by States and Political Subdivisions
Assets:
Available-for-Sale: Fair Value	0	0
Fair Value, Measurements, Recurring \| Significant Other Unobservable Inputs (Level 3) \| Debt Securities Issued by Corporations
Assets:
Available-for-Sale: Fair Value		0
Fair Value, Measurements, Recurring \| Significant Other Unobservable Inputs (Level 3) \| Mortgage-Backed Securities
Assets:
Available-for-Sale: Fair Value	0	0
Fair Value, Measurements, Recurring \| Significant Other Unobservable Inputs (Level 3) \| Residential - Government Agencies
Assets:
Available-for-Sale: Fair Value	0	0
Fair Value, Measurements, Recurring \| Significant Other Unobservable Inputs (Level 3) \| Residential - U.S. Government-Sponsored Enterprises
Assets:
Available-for-Sale: Fair Value	0	0
Fair Value, Measurements, Recurring \| Significant Other Unobservable Inputs (Level 3) \| Commercial - Government Agencies
Assets:
Available-for-Sale: Fair Value	$ 0	$ 0

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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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, 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 financial and nonfinancial obligations.

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Amount, after allowance for bad debt, of loan receivables held-for-sale that are not part of a disposal group. Excludes loans and leases covered under loss sharing agreements and loans classified as debt securities.

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Fair value portion of other assets.

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Fair value of an asset representing net future revenue from contractually specified servicing fees, late charges, and other ancillary revenues, in excess of future costs related to servicing arrangements.

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