Accounts Receivable, Net of Allowance, and Contract Assets and Liabilities (Schedule of Accounts Receivable, Net of Allowance and Contract Assets) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Receivables [Abstract]
Contract billings	$ 939,600	$ 860,400
Less allowance	(22,500)	(10,100)
Accounts receivable, net of allowance	917,099	850,326
Contract Assets [Abstract]
Retainage	313,100	345,200
Unbilled receivables	706,800	679,400
Contract assets	$ 1,019,879	$ 1,024,568