Commitments and Contingencies (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Loss Contingencies [Line Items]
Estimated Litigation Liability	$ 0.0	$ 0.0
Surety Bond [Member]
Loss Contingencies [Line Items]
Outstanding surety bonds	47.5	44.0
Surety bonds work remaining to complete	15.0	15.7
Letter of Credit [Member]
Loss Contingencies [Line Items]
Letter of Credit Facility, Maximum Borrowing Capacity	5.0
Letters of Credit Outstanding, Amount	1.8
Optional Facility Increase [Member] | Letter of Credit [Member]
Loss Contingencies [Line Items]
Letter of Credit Facility, Maximum Borrowing Capacity	7.5
Corporate Joint Venture [Member] | Financial Guarantee [Member]
Loss Contingencies [Line Items]
Long-term Debt, Gross	61.0	56.0
Loans Payable [Member] | Corporate Joint Venture [Member]
Loss Contingencies [Line Items]
Related Party Transaction, Guarantor Obligations, Underlying Asset Class Guaranteed	$ 9.6	$ 8.6