STOCK-BASED COMPENSATION - Summary of RSU Activity (Details) - USD ($) $ / shares in Units, $ in Thousands		1 Months Ended	3 Months Ended		6 Months Ended	12 Months Ended
	Aug. 08, 2019	Feb. 28, 2018	Dec. 31, 2018	Mar. 31, 2018	Jun. 30, 2019	Aug. 13, 2019	Dec. 31, 2018
Weighted-Average Grant Date Fair Value
Award vesting period					4 years
Restricted securities units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option expense					$ 26,295		$ 4,536
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost not yet recognized					3 years 5 months 1 day		2 years 5 months 1 day
Shares
Unvested — Beginning balance (in shares)					381,000
Granted (in shares)					1,714,000
Vested (in shares)					(157,000)
Forfeited (in shares)					(92,000)
Unvested — Ending balance (in shares)			381,000		1,846,000		381,000
Weighted-Average Grant Date Fair Value
Unvested — Beginning balance (in usd per share)					$ 18.11
Granted (in usd per share)					15.34
Vested (in usd per share)					17.55
Forfeited (in usd per share)					19.41
Unvested — Ending balance (in usd per share)			$ 18.11		$ 20.68		$ 18.11
Performance Shares [Member]
Shares
Vested (in shares)			(850,000,000)
Forfeited (in shares)							(25,000,000)
Unvested — Ending balance (in shares)		875,000			1,252,500
Subsequent Event | Restricted stock units
Shares
Granted (in shares)	78,191
Weighted-Average Grant Date Fair Value
Award vesting period						4 years
Compensation not yet recognized, awards other than options	$ 2,100
Maximum | Employees and non-employee directors | Restricted stock units
Weighted-Average Grant Date Fair Value
Award vesting period				4 years