Accumulated Other Comprehensive (Loss) Income Accumulated Other Comprehensive (Loss) Income (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance			$ 804.7
Other comprehensive income, net of tax			2.4
Ending balance	$ 768.8		768.8
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(36.2)	$ (30.5)	(37.1)	$ (31.3)
Reclassification from AOCI, Current Period, Tax	(0.6)	(0.4)	(1.1)	(0.8)
Reclassification from AOCI, Current Period, Net of Tax, Attributable to Parent	0.8	0.7	1.7	1.4
Defined Benefit Plan, Foreign Currency Exchange Rate Gain (Loss)	0.0	0.0	0.0	0.1
Other comprehensive income, net of tax	0.8	0.7	1.7	1.5
Ending balance	(35.4)	(29.8)	(35.4)	(29.8)
Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Reclassification from AOCI, Current Period, before Tax, Attributable to Parent	0.2	0.1	0.4	0.2
Accumulated Defined Benefit Plans Adjustment, Net Prior Service Attributable to Parent [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Reclassification from AOCI, Current Period, before Tax, Attributable to Parent	1.2	1.0	2.4	2.0
Accumulated Net Investment Gain (Loss) Attributable to Parent [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	0.9	(0.1)	0.8	(0.1)
OCI, before Reclassifications, before Tax, Attributable to Parent	1.0	0.4	2.1	0.4
Other Comprehensive Income (Loss) before Reclassifications, Tax	(0.4)	(0.1)	(0.8)	(0.1)
OCI, before Reclassifications, Net of Tax, Attributable to Parent	0.6	0.3	1.3	0.3
Reclassification from AOCI, Current Period, before Tax, Attributable to Parent	(0.7)	0.0	(1.6)	0.0
Reclassification from AOCI, Current Period, Tax	0.3	0.0	0.6	0.0
Reclassification from AOCI, Current Period, Net of Tax, Attributable to Parent	(0.4)	0.0	(1.0)	0.0
Other comprehensive income, net of tax	0.2	0.3	0.3	0.3
Ending balance	1.1	0.2	1.1	0.2
Accumulated Other Comprehensive Loss (Other) [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(0.1)	(0.2)	(0.4)	(0.3)
OCI, before Reclassifications, before Tax, Attributable to Parent	0.0	(0.1)	0.3	0.1
Other Comprehensive Income (Loss) before Reclassifications, Tax	0.0	0.0	(0.1)	(0.1)
OCI, before Reclassifications, Net of Tax, Attributable to Parent	0.0	(0.1)	0.2	0.0
Reclassification from AOCI, Current Period, before Tax, Attributable to Parent	0.1	0.0	0.3	0.0
Reclassification from AOCI, Current Period, Tax	0.0	0.0	(0.1)	0.0
Reclassification from AOCI, Current Period, Net of Tax, Attributable to Parent	0.1	0.0	0.2	0.0
Other comprehensive income, net of tax	0.1	(0.1)	0.4	0.0
Ending balance	0.0	(0.3)	0.0	(0.3)
AOCI Attributable to Parent [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance			(36.7)
Other comprehensive income, net of tax			2.4
Ending balance	$ (34.3)	$ (29.9)	$ (34.3)	$ (29.9)