Investments - Narrative (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		$ 56.4	$ 50.0
Other comprehensive (loss) income		3.7	(17.2)	$ (15.9)
Available-for-sale investments		57.7	50.7
Available-for-sale investments, realized loss	$ 5.0
Available-for-sale investments, accumulated unrealized losses		0.1	0.1
Available-for-sale investments, fair value of securities with unrealized losses		6.1	3.6
Unrealized Gain (Loss) on Available-for-Sale Securities
Debt Securities, Available-for-sale [Line Items]
Other comprehensive (loss) income		0.4	$ 2.6	$ (1.4)
State and Local Municipal Bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		$ 56.4