SHARE-BASED COMPENSATION - RSU Activity - Summary of Change (Details) $ / shares in Units, shares in Thousands, $ in Thousands	9 Months Ended
	Sep. 30, 2019 USD ($) $ / shares shares
Number of Restricted Stock Units [Roll Forward]
RSUs beginning	3,685
RSUs awarded	1,696
RSUs released	(1,373)
RSUs forfeited	(310)
RSUs ending	3,698
Weighted Average Purchase Price RSUs | $ / shares	$ 0
Weighted Average Remaining Contractual Term (Years) RSUs	1 year 6 months
Aggregate Intrinsic Value RSUs | $	$ 12,576
Number of RSUs vested and expected to vest	3,698
Weighted Average Purchase Price of RSUs vested and expected to vest | $ / shares	$ 0
Weighted Average Remaining Contractual Term (Years) of RUSs vested and expected to vest	1 year 6 months
Aggregate Intrinsic Value RSUs vested and expected to vest | $	$ 12,575
Number of RSUs exercisable	41
Weighted Average Purchase Price of RUSs exercisable | $ / shares	$ 0
Aggregate Intrinsic Value RSUs exercisable | $	$ 141
Weighted average remaining recognition period in years	2 years 4 months 24 days
Unamortized compensation expense, net of estimated forfeitures | $	$ 22,392