Accounts Receivable, Accounts Payable and Accrued Liabilities (Details 1) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accounts Receivable, after Allowance for Credit Loss [Abstract]
Receivables from contracts with customers, less doubtful accounts	$ 519,577	$ 595,321
Other receivables	17,579	28,895
Accounts receivable, net	537,156	624,216
Accounts Receivable, Allowance for Credit Loss	21,494	14,276
Accounts Payable, Current [Abstract]
Accounts payable and accrued liabilities	384,743	366,963
Accrued compensation and related benefits	135,493	140,738
Total accounts payable and accrued liabilities	520,236	507,701
Estimated Credit Losses [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	14,276	14,775	$ 22,975
Additions - Charged to Costs and Expenses	10,667	1,706	10,209
Deductions	(3,449)	(2,205)	(18,409)
Balance at End of Period	$ 21,494	$ 14,276	$ 14,775