NET INCOME PER SHARE - Narrative (Details) - shares	9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 15, 2016
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Shares excluded from computation as their effect would be anti-dilutive (in shares)	200,000	300,000
Vested Restricted Units and Vested Performance Units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted average number of shares outstanding, basic and diluted (in shares)	500,000
Convertible Debt
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Warrants exercised (in shares)			8,707,202
Common stock from the exercise of warrants (in shares)			2,839,743
Warrants outstanding (in shares)	0
2016 Senior Convertible Notes | Convertible Debt
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Interest rate on debt				1.625%