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 of Assets and Liabilities (Fair value on recurring basis) (Details 1) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Assets:
Available-for-Sale: Fair Value	$ 2,186,041	$ 2,256,818	$ 2,289,190
Loans Held for Sale	62,499	4,808
Derivative Assets	13,731	13,967
Fair Value, Measurements, Recurring [Member]
Assets:
Available-for-Sale: Fair Value	2,186,041	2,256,818
Loans Held for Sale	62,499	4,808
Mortgage Servicing Rights	1,655	1,970
Other Assets	21,952	20,262
Derivative Assets	13,731	13,967
Total Assets Measured at Fair Value on a Recurring Basis	2,285,878	2,297,825
Liabilities:
Derivative Liabilities	12,588	13,619
Total Liabilities Measured at Fair Value on a Recurring Basis	12,588	13,619
Fair Value, Measurements, Recurring [Member] \| Debt Securities Issued by the U.S. Treasury and Government Agencies
Assets:
Available-for-Sale: Fair Value	408,715	358,894
Fair Value, Measurements, Recurring [Member] \| Debt Securities Issued by States and Political Subdivisions
Assets:
Available-for-Sale: Fair Value	671,799	731,918
Fair Value, Measurements, Recurring [Member] \| Debt Securities Issued by Corporations
Assets:
Available-for-Sale: Fair Value	269,179	308,870
Fair Value, Measurements, Recurring [Member] \| Mortgage-Backed Securities
Assets:
Available-for-Sale: Fair Value	836,348	857,136
Fair Value, Measurements, Recurring [Member] \| Residential - Government Agencies
Assets:
Available-for-Sale: Fair Value	243,844	316,245
Fair Value, Measurements, Recurring [Member] \| Residential - U.S. Government Sponsored Enterprises
Assets:
Available-for-Sale: Fair Value	506,987	441,864
Fair Value, Measurements, Recurring [Member] \| Commercial - Government Agencies
Assets:
Available-for-Sale: Fair Value	85,517	99,027
Fair Value, Measurements, Recurring [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Available-for-Sale: Fair Value	539	545
Loans Held for Sale	0	0
Mortgage Servicing Rights	0	0
Other Assets	21,952	20,262
Derivative Assets	0	0
Total Assets Measured at Fair Value on a Recurring Basis	22,491	20,807
Liabilities:
Derivative Liabilities	0	0
Total Liabilities Measured at Fair Value on a Recurring Basis	0	0
Fair Value, Measurements, Recurring [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) \| Debt Securities Issued by the U.S. Treasury and Government Agencies
Assets:
Available-for-Sale: Fair Value	539	545
Fair Value, Measurements, Recurring [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) \| Debt Securities Issued by States and Political Subdivisions
Assets:
Available-for-Sale: Fair Value	0	0
Fair Value, Measurements, Recurring [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) \| Debt Securities Issued by Corporations
Assets:
Available-for-Sale: Fair Value	0	0
Fair Value, Measurements, Recurring [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) \| Mortgage-Backed Securities
Assets:
Available-for-Sale: Fair Value	0	0
Fair Value, Measurements, Recurring [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) \| Residential - Government Agencies
Assets:
Available-for-Sale: Fair Value	0	0
Fair Value, Measurements, Recurring [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) \| Residential - U.S. Government Sponsored Enterprises
Assets:
Available-for-Sale: Fair Value	0	0
Fair Value, Measurements, Recurring [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) \| Commercial - Government Agencies
Assets:
Available-for-Sale: Fair Value	0	0
Fair Value, Measurements, Recurring [Member] \| Significant Other Observable Inputs (Level 2)
Assets:
Available-for-Sale: Fair Value	2,185,502	2,256,273
Loans Held for Sale	62,499	4,808
Mortgage Servicing Rights	0	0
Other Assets	0	0
Derivative Assets	926	154
Total Assets Measured at Fair Value on a Recurring Basis	2,248,927	2,261,235
Liabilities:
Derivative Liabilities	836	46
Total Liabilities Measured at Fair Value on a Recurring Basis	836	46
Fair Value, Measurements, Recurring [Member] \| Significant Other Observable Inputs (Level 2) \| Debt Securities Issued by the U.S. Treasury and Government Agencies
Assets:
Available-for-Sale: Fair Value	408,176	358,349
Fair Value, Measurements, Recurring [Member] \| Significant Other Observable Inputs (Level 2) \| Debt Securities Issued by States and Political Subdivisions
Assets:
Available-for-Sale: Fair Value	671,799	731,918
Fair Value, Measurements, Recurring [Member] \| Significant Other Observable Inputs (Level 2) \| Debt Securities Issued by Corporations
Assets:
Available-for-Sale: Fair Value	269,179	308,870
Fair Value, Measurements, Recurring [Member] \| Significant Other Observable Inputs (Level 2) \| Mortgage-Backed Securities
Assets:
Available-for-Sale: Fair Value	836,348	857,136
Fair Value, Measurements, Recurring [Member] \| Significant Other Observable Inputs (Level 2) \| Residential - Government Agencies
Assets:
Available-for-Sale: Fair Value	243,844	316,245
Fair Value, Measurements, Recurring [Member] \| Significant Other Observable Inputs (Level 2) \| Residential - U.S. Government Sponsored Enterprises
Assets:
Available-for-Sale: Fair Value	506,987	441,864
Fair Value, Measurements, Recurring [Member] \| Significant Other Observable Inputs (Level 2) \| Commercial - Government Agencies
Assets:
Available-for-Sale: Fair Value	85,517	99,027
Fair Value, Measurements, Recurring [Member] \| Significant Other Unobservable Inputs (Level 3)
Assets:
Available-for-Sale: Fair Value	0	0
Loans Held for Sale	0	0
Mortgage Servicing Rights	1,655	1,970
Other Assets	0	0
Derivative Assets	12,805	13,813
Total Assets Measured at Fair Value on a Recurring Basis	14,460	15,783
Liabilities:
Derivative Liabilities	11,752	13,573
Total Liabilities Measured at Fair Value on a Recurring Basis	11,752	13,573
Fair Value, Measurements, Recurring [Member] \| 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 [Member] \| 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 [Member] \| Significant Other Unobservable Inputs (Level 3) \| Debt Securities Issued by Corporations
Assets:
Available-for-Sale: Fair Value	0	0
Fair Value, Measurements, Recurring [Member] \| Significant Other Unobservable Inputs (Level 3) \| Mortgage-Backed Securities
Assets:
Available-for-Sale: Fair Value	0	0
Fair Value, Measurements, Recurring [Member] \| Significant Other Unobservable Inputs (Level 3) \| Residential - Government Agencies
Assets:
Available-for-Sale: Fair Value	0	0
Fair Value, Measurements, Recurring [Member] \| Significant Other Unobservable Inputs (Level 3) \| Residential - U.S. Government Sponsored Enterprises
Assets:
Available-for-Sale: Fair Value	0	0
Fair Value, Measurements, Recurring [Member] \| Significant Other Unobservable Inputs (Level 3) \| Commercial - Government Agencies
Assets:
Available-for-Sale: Fair Value	$ 0	$ 0