Derivative Instruments and Hedging Activities Open Interest Rate Swap Contracts (Details) - Cash Flow Hedging - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Interest rate swap
Derivative [Line Items]
Notional Amounts	$ 575.0	$ 575.0
Net Unrealized Gain (Loss)	(15.1)	(18.1)
Interest Rate Swap, May 2018 to May 2021
Derivative [Line Items]
Notional Amounts	25.0	25.0
Net Unrealized Gain (Loss)	(0.1)	(0.2)
Interest Rate Swap, September 2019 to September 2023
Derivative [Line Items]
Notional Amounts	150.0	150.0
Net Unrealized Gain (Loss)	(9.7)	(11.3)
Interest Rate Swap, March 2020 to February 2023
Derivative [Line Items]
Notional Amounts	400.0	400.0
Net Unrealized Gain (Loss)	$ (5.3)	$ (6.6)