ACCOUNTS RECEIVABLE, NET (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accounts receivable, net
Accounts receivable, gross	$ 63,319	$ 98,245
Less: Allowance for doubtful accounts	(10,579)	(10,424)
Total	52,740	87,821
Bad debt expense	5,116	1,829	$ 5,514
Billed
Accounts receivable, net
Accounts receivable, gross	40,787	58,392
Unbilled
Accounts receivable, net
Accounts receivable, gross	$ 22,532	$ 39,853