REVENUE (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Schedule of revenue [Line Items]
Revenue	$ 88,795	$ 141,493	$ 305,581	$ 507,963
Service revenue
Schedule of revenue [Line Items]
Revenue	85,386	133,781	289,570	489,300
Reimbursable expenses
Schedule of revenue [Line Items]
Revenue	2,810	7,213	14,495	16,484
Non-controlling interests
Schedule of revenue [Line Items]
Revenue	$ 599	$ 499	$ 1,516	$ 2,179