Accounts Receivable, Net of Allowance (Schedule of Accounts Receivable, Net of Allowance) (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Accounts Receivable, Net of Allowance
Contract billings	$ 559,300	$ 437,300
Retainage	224,900	148,800
Costs and earnings in excess of billings	440,100	332,700
Accounts receivable, gross	1,224,300	918,800
Less allowance for doubtful accounts	(8,300)	(7,700)
Accounts receivable, net	$ 1,215,954	$ 911,106