Accounts Receivable, Net of Allowance, and Contract Assets and Liabilities (Schedule of Accounts Receivable, Net of Allowance and Contract Assets) (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Accounts Receivable, Net of Allowance, and Contract Assets [Abstract]
Contract billings	$ 753,800	$ 687,600
Less allowance for doubtful accounts	(12,400)	(16,300)
Accounts receivable, net of allowance	741,400	671,300
Retainage	292,200	230,200
Costs and earnings in excess of billings	952,700	1,022,500
Retainage and costs and earnings in excess of billings (together, “contract assets”)	1,244,900	1,252,700
Accounts receivable, net	$ 1,986,335	$ 1,923,970