REVENUE RECOGNITION - NARRATIVE (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue recognized, true up	$ 149	$ 0
Fixed fee license revenue recognized	$ 1,100
Fixed fee license revenue | Minimum
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, payment terms	30 days
Fixed fee license revenue | Maximum
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, payment terms	45 days
Per-unit royalty revenue | Minimum
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, payment terms	30 days
Per-unit royalty revenue | Maximum
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, payment terms	60 days