SHARE-BASED COMPENSATION - RSU Activity - Summary of Change (Details) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($) $ / shares shares
Number of Restricted Stock Units [Roll Forward]
RSUs beginning	3,685
RSUs awarded	1,489
RSUs assumed in Merger	0
RSUs released	(636)
RSUs forfeited	(83)
RSUs ending	4,455
Weighted Average Purchase Price RSUs | $ / shares	$ 0
Weighted Average Remaining Contractual Term (Years) RSUs	1 year 7 months 6 days
Aggregate Intrinsic Value RSUs | $	$ 23,350
Number of RSUs vested and expected to vest	4,455
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 7 months 6 days
Aggregate Intrinsic Value RSUs vested and expected to vest | $	$ 23,347
Number of RSUs exercisable	41
Weighted Average Purchase Price of RUSs exercisable | $ / shares	$ 0
Weighted Average Remaining Contractual Term (Years) of RUSs exercisable	0 years
Aggregate Intrinsic Value RSUs exercisable | $	$ 217
Weighted average remaining recognition period in years	2 years 6 months
Unamortized compensation expense, net of estimated forfeitures | $	$ 27,619