Commitments and Contingencies (Details Textual) $ in Millions	Jun. 30, 2018 USD ($)
Other Commitments [Line Items]
Outstanding Performance Bonds	$ 606.1
Estimated Cost to Complete Bonded Projects	247.3
Purchase Commitment, Remaining Minimum Amount Committed	7.3
Maximum [Member]
Other Commitments [Line Items]
Loss Contingency Insurance Policy Deductible for Each Line of Coverage Excluding Wildfire and Health	1.0
Loss Contingency Insurance Policy Deductible for Wildfire	2.0
Loss Contingency Health Insurance Deductible For Qualified Individuals	$ 0.2