Accounts Receivable, Net of Allowance (Schedule of Accounts Receivable, Net of Allowance) (Details) - USD ($) $ in Thousands	Mar. 31, 2015	Dec. 31, 2014
Accounts Receivable, Net of Allowance
Contract billings	$ 552,100	$ 669,700
Retainage	152,600	162,200
Costs and earnings in excess of billings	436,300	485,600
Accounts receivable, gross	1,141,000	1,317,500
Less allowance for doubtful accounts	(8,200)	(13,900)
Accounts receivable, net	$ 1,132,832	$ 1,303,552