Derivative and Hedging Activities Cumulative Basis Adjustment for Fair Value Hedges (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Balance Sheet Recording of Fair Value Hedge [Line Items]
Carrying Amount of the Hedged Assets/(Liabilities)	$ 77,920	$ 88,943
Designated as Hedging Instrument
Balance Sheet Recording of Fair Value Hedge [Line Items]
Carrying Amount of the Hedged Assets/(Liabilities)	500,000
Cumulative Amount of Fair Value Hedging Adjustment Included in the Carrying Amount of the Hedged Assets/(Liabilities)	2,000
Amortized cost basis of hedged asset	1,100,000
Carrying Value [Member] | Designated as Hedging Instrument
Balance Sheet Recording of Fair Value Hedge [Line Items]
Carrying Amount of the Hedged Assets/(Liabilities)	501,555
adjustment [Member] | Designated as Hedging Instrument
Balance Sheet Recording of Fair Value Hedge [Line Items]
Cumulative Amount of Fair Value Hedging Adjustment Included in the Carrying Amount of the Hedged Assets/(Liabilities)	$ 1,555