Accounts Receivable, Net of Allowance (Schedule of Accounts Receivable, Net of Allowance) (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Accounts Receivable, Net of Allowance
Contract billings	$ 478,900	$ 437,300
Retainage	145,500	148,800
Costs and earnings in excess of billings	354,000	332,700
Accounts receivable, gross	978,400	918,800
Less allowance for doubtful accounts	(7,500)	(7,700)
Accounts receivable, net	$ 970,886	$ 911,106