Commitments and Contingencies (Narrative) (Details)			6 Months Ended
	Feb. 28, 2017 USD ($)	Jan. 14, 2015 USD ($)	Jun. 30, 2019 USD ($) bbl	May 31, 2017 USD ($)
Commitments And Contingencies [Line Items]
Outstanding performance bonds			$ 1,249,824,000
Revenue value remaining from outstanding performance bonds			$ 442,475,000
Proceeds from Legal Settlements		$ 5,309,000
Crude Oil [Member]
Commitments And Contingencies [Line Items]
Quantity of oil spill | bbl			125
Surety Bond [Member]
Commitments And Contingencies [Line Items]
Aggregate demolition surety performance bond	$ 20,000,000
Letter of Credit [Member]
Commitments And Contingencies [Line Items]
Line of credit facility, maximum borrowing capacity				$ 20,881,000
Environmental and Infrastructure Segment [Member]
Commitments And Contingencies [Line Items]
Outstanding performance bonds			$ 41,085,000
Minimum [Member]
Commitments And Contingencies [Line Items]
Bids bond range			$ 1,000,000
Warranty periods			1 year
Loss contingency, Estimate of possible loss			$ 200,000
Maximum [Member]
Commitments And Contingencies [Line Items]
Bids bond range			$ 10,000,000
Warranty periods			3 years
Loss contingency, Estimate of possible loss			$ 250,000