Fair Value of Assets and Liabilities (Fair value on recurring basis) (Details 1) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Assets:
Available-for-Sale: Fair Value	$ 2,594,394	$ 2,007,942
Loans Held for Sale	36,720	10,987
Debt Securities Issued by States and Political Subdivisions
Assets:
Available-for-Sale: Fair Value	53,982	563,996
Debt Securities Issued by Government-Sponsored Enterprises
Assets:
Available-for-Sale: Fair Value	21,895	56
Debt Securities Issued by Corporations
Assets:
Available-for-Sale: Fair Value	348,441	223,140
Mortgage-Backed Securities
Assets:
Available-for-Sale: Fair Value	1,934,391	828,349
Residential - Government Agencies
Assets:
Available-for-Sale: Fair Value	1,228,637	190,442
Residential - U.S. Government-Sponsored Enterprises
Assets:
Available-for-Sale: Fair Value	537,336	578,527
Commercial - Government Agencies
Assets:
Available-for-Sale: Fair Value	168,418	59,380
Fair Value, Measurements, Recurring
Assets:
Available-for-Sale: Fair Value	2,594,394	2,007,942
Loans Held for Sale	36,720	10,987
Mortgage Servicing Rights	1,174	1,290
Other Assets	37,865	31,871
Derivatives	40,692	14,604
Total Assets Measured at Fair Value on a Recurring Basis	2,710,845	2,066,694
Liabilites:
Derivatives	9,438	9,747
Total Liabilities Measured at Fair Value on a Recurring Basis	9,438	9,747
Fair Value, Measurements, Recurring | Debt Securities Issued by the U.S. Treasury and Government Agencies
Assets:
Available-for-Sale: Fair Value	235,685	392,401
Fair Value, Measurements, Recurring | Debt Securities Issued by States and Political Subdivisions
Assets:
Available-for-Sale: Fair Value	53,982	563,996
Fair Value, Measurements, Recurring | Debt Securities Issued by Government-Sponsored Enterprises
Assets:
Available-for-Sale: Fair Value	21,895	56
Fair Value, Measurements, Recurring | Debt Securities Issued by Corporations
Assets:
Available-for-Sale: Fair Value	348,441	223,140
Fair Value, Measurements, Recurring | Mortgage-Backed Securities
Assets:
Available-for-Sale: Fair Value	1,934,391	828,349
Fair Value, Measurements, Recurring | Residential - Government Agencies
Assets:
Available-for-Sale: Fair Value	1,228,637	190,442
Fair Value, Measurements, Recurring | Residential - U.S. Government-Sponsored Enterprises
Assets:
Available-for-Sale: Fair Value	537,336	578,527
Fair Value, Measurements, Recurring | Commercial - Government Agencies
Assets:
Available-for-Sale: Fair Value	168,418	59,380
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)
Assets:
Available-for-Sale: Fair Value	1,005	972
Loans Held for Sale	0	0
Mortgage Servicing Rights	0	0
Other Assets	37,865	31,871
Derivatives	0	0
Total Assets Measured at Fair Value on a Recurring Basis	38,870	32,843
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	1,005	972
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	2,593,389	2,006,970
Loans Held for Sale	36,720	10,987
Mortgage Servicing Rights	0	0
Other Assets	0	0
Derivatives	432	812
Total Assets Measured at Fair Value on a Recurring Basis	2,630,541	2,018,769
Liabilites:
Derivatives	1,089	371
Total Liabilities Measured at Fair Value on a Recurring Basis	1,089	371
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	234,680	391,429
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Debt Securities Issued by States and Political Subdivisions
Assets:
Available-for-Sale: Fair Value	53,982	563,996
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Debt Securities Issued by Government-Sponsored Enterprises
Assets:
Available-for-Sale: Fair Value	21,895	56
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Debt Securities Issued by Corporations
Assets:
Available-for-Sale: Fair Value	348,441	223,140
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Mortgage-Backed Securities
Assets:
Available-for-Sale: Fair Value	1,934,391	828,349
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Residential - Government Agencies
Assets:
Available-for-Sale: Fair Value	1,228,637	190,442
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Residential - U.S. Government-Sponsored Enterprises
Assets:
Available-for-Sale: Fair Value	537,336	578,527
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Commercial - Government Agencies
Assets:
Available-for-Sale: Fair Value	168,418	59,380
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	1,174	1,290
Other Assets	0	0
Derivatives	40,260	13,792
Total Assets Measured at Fair Value on a Recurring Basis	41,434	15,082
Liabilites:
Derivatives	8,349	9,376
Total Liabilities Measured at Fair Value on a Recurring Basis	8,349	9,376
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