ACCRUED LIABILITIES - Schedule of Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Accounts Payable and Accrued Liabilities, Current [Abstract]
Accrued compensation	$ 5,475	$ 7,345
Accrued royalties	2,773	17,370
Accrued restructuring and one-time termination costs	1,578	9,483
Other accrued liabilities	21,535	26,298
Total accrued liabilities	$ 31,361	$ 60,496