Variable Interest Entities (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Variable Interest Entity [Line Items]
Assets, current	$ 4,111,967		$ 4,111,967		$ 3,510,986
Liabilities, current	2,352,310		2,352,310		2,109,856
Revenue	$ 1,442,091	$ 1,189,345	$ 3,969,247	$ 3,273,107
Purple Line Extension Section 2 And Section 3
Variable Interest Entity [Line Items]
Percent interest in the joint venture			75.00%
Newark Airport Terminal One Design Build Project
Variable Interest Entity [Line Items]
Percent interest in the joint venture			80.00%
Joint Venture With O&G Industries | Purple Line Extension Section 2 And Section 3
Variable Interest Entity [Line Items]
Revenue			$ 2,800,000
O&G | Purple Line Extension Section 2 And Section 3
Variable Interest Entity [Line Items]
Noncontrolling interest, ownership percentage by noncontrolling owners	25.00%		25.00%
Joint Venture With Parsons | Newark Airport Terminal One Design Build Project
Variable Interest Entity [Line Items]
Revenue			$ 1,400,000
Parsons Corporation | Newark Airport Terminal One Design Build Project
Variable Interest Entity [Line Items]
Noncontrolling interest, ownership percentage by noncontrolling owners	20.00%		20.00%
Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Assets, current	$ 800		$ 800		1,500
Liabilities, current	700		700		1,400
Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Assets, current	417,500		417,500		365,000
Liabilities, current	550,100		550,100		556,100
Assets, noncurrent	$ 19,200		$ 19,200		$ 52,000