SHARE-BASED COMPENSATION - Stock Option Activity (Details) - 2017 LTIP - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Weighted Average Exercise Price Per Share
Beginning balance (in dollars per share)	$ 17.50
Granted (in dollars per share)	23.43
Forfeited (in dollars per share)	17.85
Ending balance (in dollars per share)	18.80	$ 17.50
Options exercisable (in dollars per share)	$ 0
Options outstanding, Weighted Average Remaining Contractual Term (in years)	8 years 11 months 4 days	9 years 5 months 19 days
Options exercisable, Weighted Average Remaining Contractual Term (in years)	0 years
Options outstanding, Aggregate Intrinsic Value		$ 0
Options exercisable, Aggregate Intrinsic Value	$ 138,194
Time Vesting
Shares Under Option
Beginning balance (in shares)	11,230,168
Granted (in shares)	3,091,573
Forfeited (in shares)	(393,670)
Ending balance (in shares)	13,928,071	11,230,168
Options exercisable (in shares)	0
Performance Based Vesting
Shares Under Option
Beginning balance (in shares)	73,639
Granted (in shares)	0
Forfeited (in shares)	(16,736)
Ending balance (in shares)	56,903	73,639
Options exercisable (in shares)	0