Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Operating Loss Carryforwards
Tax benefit from changes in enacted taxes			$ 22.5
One-time provisional tax benefit			26.9
Provisional deemed repatriation transition tax			8.7
Provisional decrease of deferred tax liabilities			26.9
Income tax expense (benefit)	$ 2.3	$ (1.8)
Effective income tax rate (percent)	26.70%	37.40%
Effective federal statutory rate (percent)	21.00%	35.00%
Liability for gross unrecognized tax benefits	$ 1.1		0.8
Unrecognized tax benefit that would impact effective tax rate	1.0		0.6
Accrual for interest and penalties	$ 0.2		0.1
Hudson
Operating Loss Carryforwards
Provisional deemed repatriation transition tax			(4.5)
One-time provisional tax benefit			$ 8.7