Fair Value of Assets and Liabilities (Fair value on recurring basis) (Details 1) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Assets:
Available-for-Sale: Fair Value	$ 2,681,049	$ 2,619,003
Loans Held for Sale	20,789	39,062
Debt Securities Issued by States and Political Subdivisions
Assets:
Available-for-Sale: Fair Value	55,023	55,097
Debt Securities Issued by Government-Sponsored Enterprises
Assets:
Available-for-Sale: Fair Value	1,012	22,147
Debt Securities Issued by Corporations
Assets:
Available-for-Sale: Fair Value	271,176	336,321
Mortgage-Backed Securities
Assets:
Available-for-Sale: Fair Value	2,152,749	1,984,307
Residential - Government Agencies
Assets:
Available-for-Sale: Fair Value	1,199,214	1,172,826
Residential - U.S. Government-Sponsored Enterprises
Assets:
Available-for-Sale: Fair Value	661,173	586,761
Commercial - Government Agencies
Assets:
Available-for-Sale: Fair Value	292,362	224,720
Fair Value, Measurements, Recurring
Assets:
Available-for-Sale: Fair Value	2,681,049	2,619,003
Loans Held for Sale	20,789	39,062
Mortgage Servicing Rights	1,101	1,126
Other Assets	42,844	41,464
Derivatives	100,591	28,931
Total Assets Measured at Fair Value on a Recurring Basis	2,846,374	2,729,586
Liabilites:
Derivatives	21,051	6,377
Total Liabilities Measured at Fair Value on a Recurring Basis	21,051	6,377
Fair Value, Measurements, Recurring | Debt Securities Issued by the U.S. Treasury and Government Agencies
Assets:
Available-for-Sale: Fair Value	201,089	221,131
Fair Value, Measurements, Recurring | Debt Securities Issued by States and Political Subdivisions
Assets:
Available-for-Sale: Fair Value	55,023	55,097
Fair Value, Measurements, Recurring | Debt Securities Issued by Government-Sponsored Enterprises
Assets:
Available-for-Sale: Fair Value	1,012	22,147
Fair Value, Measurements, Recurring | Debt Securities Issued by Corporations
Assets:
Available-for-Sale: Fair Value	271,176	336,321
Fair Value, Measurements, Recurring | Mortgage-Backed Securities
Assets:
Available-for-Sale: Fair Value	2,152,749	1,984,307
Fair Value, Measurements, Recurring | Residential - Government Agencies
Assets:
Available-for-Sale: Fair Value	1,199,214	1,172,826
Fair Value, Measurements, Recurring | Residential - U.S. Government-Sponsored Enterprises
Assets:
Available-for-Sale: Fair Value	661,173	586,761
Fair Value, Measurements, Recurring | Commercial - Government Agencies
Assets:
Available-for-Sale: Fair Value	292,362	224,720
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)
Assets:
Available-for-Sale: Fair Value	1,176	1,155
Loans Held for Sale	0	0
Mortgage Servicing Rights	0	0
Other Assets	42,844	41,464
Derivatives	0	0
Total Assets Measured at Fair Value on a Recurring Basis	44,020	42,619
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	1,176	1,155
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 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) | 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	2,679,873	2,617,848
Loans Held for Sale	20,789	39,062
Mortgage Servicing Rights	0	0
Other Assets	0	0
Derivatives	743	308
Total Assets Measured at Fair Value on a Recurring Basis	2,701,405	2,657,218
Liabilites:
Derivatives	1,883	327
Total Liabilities Measured at Fair Value on a Recurring Basis	1,883	327
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	199,913	219,976
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Debt Securities Issued by States and Political Subdivisions
Assets:
Available-for-Sale: Fair Value	55,023	55,097
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Debt Securities Issued by Government-Sponsored Enterprises
Assets:
Available-for-Sale: Fair Value	1,012	22,147
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Debt Securities Issued by Corporations
Assets:
Available-for-Sale: Fair Value	271,176	336,321
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Mortgage-Backed Securities
Assets:
Available-for-Sale: Fair Value	2,152,749	1,984,307
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Residential - Government Agencies
Assets:
Available-for-Sale: Fair Value	1,199,214	1,172,826
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Residential - U.S. Government-Sponsored Enterprises
Assets:
Available-for-Sale: Fair Value	661,173	586,761
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Commercial - Government Agencies
Assets:
Available-for-Sale: Fair Value	292,362	224,720
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	1,101	1,126
Other Assets	0	0
Derivatives	99,848	28,623
Total Assets Measured at Fair Value on a Recurring Basis	100,949	29,749
Liabilites:
Derivatives	19,168	6,050
Total Liabilities Measured at Fair Value on a Recurring Basis	19,168	6,050
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 Government-Sponsored Enterprises
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	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