Accounts Receivable, Net of Allowance, and Contract Assets and Liabilities (Schedule of Accounts Receivable, Net of Allowance, and Contract Assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Receivables [Abstract]
Contract billings	$ 805,000	$ 860,400
Less allowance	(20,500)	(10,100)
Accounts receivable, net of allowance	784,488	850,326
Accounts Receivable, Net of Allowance, and Contract Assets [Abstract]
Retainage	287,700	345,200
Unbilled receivables	682,000	679,400
Contract assets	$ 969,743	$ 1,024,568