Shareholders' Equity - Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance			$ (26.7)
Other comprehensive income (loss) before reclassifications, net of tax			(0.2)
Amounts reclassified from accumulated other comprehensive income, net of tax			0.2
Total other comprehensive income (loss), net of tax	$ 0.2	$ 0.1	0.0	$ 0.2
Ending balance	(29.8)		(29.8)
Defined Benefit Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance			(18.2)
Other comprehensive income (loss) before reclassifications, net of tax			0.0
Amounts reclassified from accumulated other comprehensive income, net of tax			0.2
Total other comprehensive income (loss), net of tax			0.2
Ending balance	(18.0)		(18.0)
Foreign Currency Translation
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance			(0.7)
Other comprehensive income (loss) before reclassifications, net of tax			(0.2)
Amounts reclassified from accumulated other comprehensive income, net of tax			0.0
Total other comprehensive income (loss), net of tax			(0.2)
Ending balance	(0.9)		(0.9)
Total
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance			(18.9)
Ending balance	$ (18.9)		$ (18.9)