SHARE-BASED COMPENSATION - RSU Activity - Summary of Change (Details) $ / shares in Units, shares in Thousands, $ in Thousands	6 Months Ended
	Jun. 30, 2019 USD ($) $ / shares shares
Number of Restricted Stock Units [Roll Forward]
RSUs beginning	3,685
RSUs awarded	1,648
RSUs released	(1,367)
RSUs forfeited	(280)
RSUs ending	3,686
Weighted Average Purchase Price RSUs | $ / shares	$ 0
Weighted Average Remaining Contractual Term (Years) RSUs	1 year 8 months 12 days
Aggregate Intrinsic Value RSUs | $	$ 21,308
Number of RSUs vested and expected to vest	3,686
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 8 months 12 days
Aggregate Intrinsic Value RSUs vested and expected to vest | $	$ 21,306
Number of RSUs exercisable	41
Weighted Average Purchase Price of RUSs exercisable | $ / shares	$ 0
Aggregate Intrinsic Value RSUs exercisable | $	$ 239
Weighted average remaining recognition period in years	2 years 8 months 12 days
Unamortized compensation expense, net of estimated forfeitures | $	$ 25,392