Accounts Receivable, Net of Allowance (Schedule of Accounts Receivable, Net of Allowance) (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Accounts Receivable, Net of Allowance
Contract billings	$ 526,800	$ 437,300
Retainage	175,600	148,800
Costs and earnings in excess of billings	398,200	332,700
Accounts receivable, gross	1,100,600	918,800
Less allowance for doubtful accounts	(9,600)	(7,700)
Accounts receivable, net	$ 1,091,025	$ 911,106