Income Taxes - Loss carryforwards (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Tax Credit Carryforward [Line Items]
Statutory income tax rate, as a percent	21.00%	21.00%	35.00%
Domestic Tax Authority [Member]
Tax Credit Carryforward [Line Items]
Operating Loss Carryforwards, Total	$ 64.3	$ 177.7
Operating loss carryforwards subject to expiration	24.6
Operating loss carryforwards not subject to expiration	39.7
Tax credits subject to expiration	11.0
State and Local Jurisdiction [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Amount	0.5	0.6
Operating Loss Carryforwards, Total	138.8	122.3
Operating loss carryforwards subject to expiration	138.8
Tax credits subject to expiration	0.5
Capital Loss Carryforward [Member] | Domestic Tax Authority [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Amount	$ 22.0	$ 0.0