ACCOUNTS RECEIVABLE, NET (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accounts receivable, net
Accounts receivable, gross	$ 27,994	$ 48,087
Less: Allowance for credit losses	(5,581)	(4,472)
Total	22,413	43,615
Bad debt expense	2,229	720	$ 2,830
Billed
Accounts receivable, net
Accounts receivable, gross	19,703	35,921
Unbilled
Accounts receivable, net
Accounts receivable, gross	$ 8,291	$ 12,166