Accounts Receivable, Net of Allowance (Schedule of Accounts Receivable, Net of Allowance) (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Accounts Receivable, Net of Allowance
Contract billings	$ 512,300	$ 669,700
Retainage	164,000	162,200
Costs and earnings in excess of billings	356,000	485,600
Accounts receivable, gross	1,032,300	1,317,500
Less allowance for doubtful accounts	(8,600)	(13,900)
Accounts receivable, net	$ 1,023,663	$ 1,303,552