Accounts Receivable, Net and Contract Assets and Liabilities (Schedule of Accounts Receivable, Net and Contract Assets and Liabilities) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Accounts Receivable, Net and Contract Assets and Liabilities [Abstract]
Contract billings	$ 679,400	$ 683,900
Less allowance for doubtful accounts	(9,000)	(8,200)
Accounts receivable, net of allowance	670,400	675,700
Retainage	301,900	323,100
Costs and earnings in excess of billings	732,800	599,200
Retainage and costs and earnings in excess of billings (together, “contract assets”)	1,034,700	922,300
Accounts receivable, net	1,705,126	1,598,015
Billings in excess of costs and earnings	215,707	194,494
Accrued project losses	6,700	11,600
Contract liabilities	$ 222,400	$ 206,100