Derivative Instruments and Hedging Activities Open Interest Rate Swap Contracts (Details) - Cash Flow Hedging - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Interest rate swap
Derivative [Line Items]
Notional Amounts	$ 575,000	$ 275,000
Net Unrealized Gain (Loss)	(20,000)	(8,000)
Interest Rate Swap, May 2018 to May 2021
Derivative [Line Items]
Notional Amounts	25,000	25,000
Net Unrealized Gain (Loss)	(300)	(100)
Interest Rate Swap, September 2019 to September 2023
Derivative [Line Items]
Notional Amounts	150,000	150,000
Net Unrealized Gain (Loss)	(12,400)	(7,700)
Interest Rate Swap, May 2019 to May 2020
Derivative [Line Items]
Notional Amounts	0	100,000
Net Unrealized Gain (Loss)	0	(200)
Interest Rate Swap, March 2020 to February 2023
Derivative [Line Items]
Notional Amounts	400,000	0
Net Unrealized Gain (Loss)	$ (7,300)	$ 0