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, 2021	Dec. 31, 2020
Receivables [Abstract]
Contract billings	$ 965,500	$ 805,000
Less allowance	(8,500)	(20,500)
Accounts receivable, net of allowance	956,973	784,488
Contract Assets [Abstract]
Retainage	302,300	287,700
Unbilled receivables	863,900	682,000
Contract assets	$ 1,166,183	$ 969,743