Schedule II - Valuation and Qualifying Accounts and Reserves (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reserve for doubtful accounts
Movement in Valuation Allowances and Reserves
Balance, Beginning of Year	$ 0.3	$ 0.1	$ 0.5
Charged to Costs and Expenses	0.1	0.2	(0.4)
Write-offs	0.0	0.0	0.0
Balance, End of Year	0.4	0.3	0.1
Deferred tax valuation allowance
Movement in Valuation Allowances and Reserves
Balance, Beginning of Year	18.8	6.6	4.8
Charged to Costs and Expenses	1.7	13.2	1.5
Charged to Other Comprehensive Income	(0.1)	(1.0)	0.3
Write-offs	0.0	0.0
Balance, End of Year	$ 20.4	$ 18.8	$ 6.6