Accounts Receivable, Net of Allowance (Schedule of Accounts Receivable, Net of Allowance) (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Accounts Receivable, Net of Allowance
Contract billings	$ 515,000	$ 564,200
Retainage	244,300	268,600
Costs and earnings in excess of billings	335,400	331,600
Accounts receivable, gross	1,094,700	1,164,400
Less allowance for doubtful accounts	(8,600)	(8,400)
Accounts receivable, net	$ 1,086,108	$ 1,156,031