REVENUE (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Schedule of revenue [Line Items]
Revenue	$ 43,243	$ 88,795	$ 139,749	$ 305,581
Service revenue
Schedule of revenue [Line Items]
Revenue	41,626	85,386	133,672	289,570
Reimbursable expenses
Schedule of revenue [Line Items]
Revenue	1,416	2,810	5,365	14,495
Non-controlling interests
Schedule of revenue [Line Items]
Revenue	$ 201	$ 599	$ 712	$ 1,516