Investments - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Unrealized gain (loss) on investments, net of taxes of ($0.2), $0.4 and ($0.2)	$ 2.6	$ (1.4)	$ 0.6
State and Local Municipal Bonds
Debt Securities, Available-for-sale [Line Items]
Available-for-sale investment, amortized cost basis	$ 50.0