Commitments and Contingencies (Details Textual) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Other Commitments [Line Items]
Loss Contingency Insurance Policy Deductible for Each Line of Coverage Excluding Health	$ 1.0
Outstanding Performance Bonds	887.7
Estimated Cost to Complete Bonded Projects	58.2
Purchase Commitment, Remaining Minimum Amount Committed	8.6
Insurance Claims [Member]
Other Commitments [Line Items]
Loss Contingency Insurance Expense	25.6	$ 23.6	$ 21.0
Maximum [Member]
Other Commitments [Line Items]
Loss Contingency Health Insurance Deductible For Qualified Individuals	$ 0.2