Accounts Receivable, Net of Allowance (Schedule of Accounts Receivable, Net of Allowance) (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Accounts Receivable, Net of Allowance
Contract billings	$ 585,300	$ 669,700
Retainage	159,200	162,200
Costs and earnings in excess of billings	390,400	485,600
Accounts receivable, gross	1,134,900	1,317,500
Less allowance for doubtful accounts	(8,000)	(13,900)
Accounts receivable, net	$ 1,126,927	$ 1,303,552