Derivatives and Hedging Activities Non-designated Hedges Text description (Details) - Not Designated as Hedging Instrument [Member] $ in Millions	6 Months Ended
	Jun. 30, 2018 USD ($) contracts	Dec. 31, 2017 USD ($) contracts
Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Number of Instruments Held | contracts	156	142
Derivative, Notional Amount | $	$ 1,200.0	$ 1,100.0
Foreign Exchange Contract [Member]
Derivative [Line Items]
Derivative, Number of Instruments Held | contracts	11	3
Derivative, Notional Amount | $	$ 0.7	$ 0.2
Loan Participations and Assignments [Member]
Derivative [Line Items]
Derivative, Number of Instruments Held | contracts	7	6
Derivative, Notional Amount | $	$ 60.2	$ 48.0
Derivative, Underlying Risk, Description	The Bank has no obligations under the risk participation agreements unless the borrower defaults on their swap transaction with the lead bank and the swap is in a liability position to the borrower. In that instance, the Bank has agreed to pay the lead bank a portion of the swap’s termination value at the time of the default.
Other Contract [Member]
Derivative [Line Items]
Derivative, Number of Instruments Held | contracts	3	2
Derivative, Notional Amount | $	$ 11.5	$ 6.1
Derivative, Underlying Risk, Description	The other financial institution has no obligations under the risk participation agreements unless the borrowers default on their swap transactions with the Bank and the swaps are in liability positions to the borrower. In those instances, the other financial institution has agreed to pay the Bank a portion of the swap’s termination value at the time of the default.