Investments - Amortized Cost and Fair Values (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Cost or Amortized Cost	$ 71.3	$ 6.4
Gross Unrealized Gains	0.1	0.2
Gross Unrealized Losses	0.2	0.0
Fair Value	71.2	6.6
U.S. Government obligations
Debt Securities, Available-for-sale [Line Items]
Cost or Amortized Cost	71.3	6.4
Gross Unrealized Gains	0.1	0.2
Gross Unrealized Losses	0.2	0.0
Fair Value	$ 71.2	$ 6.6