Accounts Receivable, Net of Allowance, and Contract Assets and Liabilities (Schedule of Accounts Receivable, Net of Allowance and Contract Assets) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Accounts Receivable, Net of Allowance, and Contract Assets [Abstract]
Contract billings	$ 520,800	$ 683,900
Less allowance for doubtful accounts	(11,600)	(8,200)
Accounts receivable, net of allowance	509,200	675,700
Retainage	320,800	323,100
Costs and earnings in excess of billings	1,538,600	599,200
Retainage and costs and earnings in excess of billings (together, “contract assets”)	1,859,400	922,300
Accounts receivable, net	$ 2,368,597	$ 1,598,015