Goodwill and Other Intangible Assets - Gross and Net Intangible Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 200.6	$ 200.6
Accumulated Amortization	32.7	21.6
Total	$ 167.9	179.0
Customer contracts
Finite-Lived Intangible Assets [Line Items]
Weighted - Average Remaining Amortization (in years)	5 years
Gross Carrying Amount	$ 31.7	31.7
Accumulated Amortization	13.8	9.9
Total	$ 17.9	21.8
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Weighted - Average Remaining Amortization (in years)	14 years
Gross Carrying Amount	$ 28.7	28.7
Accumulated Amortization	5.7	3.8
Total	$ 23.0	24.9
Permits
Finite-Lived Intangible Assets [Line Items]
Weighted - Average Remaining Amortization (in years)	25 years
Gross Carrying Amount	$ 139.0	139.0
Accumulated Amortization	12.2	7.1
Total	$ 126.8	131.9
Trade name
Finite-Lived Intangible Assets [Line Items]
Weighted - Average Remaining Amortization (in years)	1 year
Gross Carrying Amount	$ 1.2	1.2
Accumulated Amortization	1.0	0.8
Total	$ 0.2	$ 0.4