Derivative and Hedging Activities Cumulative Basis Adjustment for Fair Value Hedges (Details) - Designated as Hedging Instrument $ in Thousands	Sep. 30, 2019 USD ($)
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)	$ 6,000
Amortized cost basis of hedged asset	947,000
Derivative Asset, Notional Amount	500,000
Carrying Amount of the Hedged Assets/(Liabilities)
Balance Sheet Recording of Fair Value Hedge [Line Items]
Derivative Asset	506,111
Cumulative Amount of Fair Value Hedging Adjustment Included in the Carrying Amount of the Hedged Assets/(Liabilities)
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)	$ 6,111