Accounts Receivable, Net of Allowance (Schedule of Accounts Receivable, Net of Allowance) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accounts Receivable, Net of Allowance
Contract billings	$ 564,200	$ 437,300
Retainage	268,600	148,800
Cost and earnings in excess of billings	331,600	332,700
Accounts receivable, gross	1,164,400	918,800
Less allowance for doubtful accounts	(8,400)	(7,700)	$ (13,900)
Accounts receivable, net	$ 1,156,031	$ 911,106