CONDENSED CONSOLIDATED BALANCE SHEETS (Unaudited) (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018
Cash and cash equivalents	$ 144,958	$ 272,804	$ 195,515
Receivables, Net	551,958	473,246	492,718
Contract assets	257,650	219,754	265,190
Other current assets	63,056	48,731	49,100
Property and equipment, net	557,118	549,688	595,787
Accounts payable	303,128	251,481	303,885
Contract liabilities	119,289	105,449	91,864
Accrued expenses and other current liabilities	$ 339,047	$ 273,626	$ 293,959
Preferred Stock, Par or Stated Value Per Share	$ 0.01	$ 0.01	$ 0.01
Preferred Stock, Shares Authorized	3,000,000	3,000,000	3,000,000
Preferred Stock, Shares Outstanding	0	0	0
Common Stock, Par or Stated Value Per Share	$ 0.01	$ 0.01	$ 0.01
Common Stock, Shares Authorized	150,000,000	150,000,000	150,000,000
Common Stock, Shares, Issued	46,838,199	46,665,889	45,688,582
Common Stock, Shares, Outstanding	46,838,199	46,665,889	45,688,582
Equity Method Investee [Member] | Construction [Member]
Cash and cash equivalents	$ 115,933	$ 131,965	$ 82,047
Receivables, Net	31,656	21,237	38,828
Contract assets	23,500	19,699	24,479
Other current assets	11,440	11,744	12,421
Property and equipment, net	31,560	34,761	38,854
Accounts payable	50,338	37,086	35,375
Contract liabilities	29,055	60,288	40,678
Accrued expenses and other current liabilities	$ 4,017	$ 2,046	$ 2,147