Accounts Receivable, Net of Allowance, and Contract Assets and Liabilities (Schedule of Accounts Receivable, Net of Allowance and Contract Assets) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Receivables [Abstract]
Contract billings	$ 806,000	$ 860,400
Less allowance	(9,900)	(10,100)
Accounts receivable, net of allowance	796,120	850,326
Accounts Receivable, Net of Allowance, and Contract Assets [Abstract]
Retainage	288,500	345,200
Unbilled receivables	709,400	679,400
Contract assets	$ 997,901	$ 1,024,568