Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Operating Loss Carryforwards
Tax benefit from changes in enacted taxes					$ 22.5
Provisional decrease of deferred tax liabilities					26.9
Provisional deemed repatriation transition tax					8.7
One-time provisional tax benefit					26.9
Income tax expense	$ 5.0	$ 2.2	$ 7.3	$ 0.4
Effective income tax rate (percent)	27.60%	39.80%	27.30%	53.60%
Effective federal statutory rate (percent)	21.00%	35.00%	21.00%	35.00%
Liability for gross unrecognized tax benefits	$ 1.1		$ 1.1		0.8
Unrecognized tax benefit that would impact effective tax rate	1.0		1.0		0.6
Accrual for interest and penalties	$ 0.2		$ 0.2		0.1
Hudson
Operating Loss Carryforwards
Provisional deemed repatriation transition tax					8.7
Additional taxes related to proposed merger					$ 4.5