ACCRUED LIABILITIES - Schedule of Accrued Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Accounts Payable and Accrued Liabilities, Current [Abstract]
Accrued compensation	$ 5,677	$ 5,475
Accrued royalties	5,799	2,773
Accrued restructuring and one-time termination costs	435	1,578
Accrued taxes payable	9,139	0
Other accrued liabilities	12,220	21,535
Total accrued liabilities	$ 33,270	$ 31,361