NET INCOME (LOSS) PER SHARE - OUTSTANDING SECURITIES (Details) - $ / shares shares in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Options to purchase shares of common stock (in shares)	2,035	2,311
RSUs
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Options to purchase shares of common stock (in shares)	753	1,205
RSAs
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Options to purchase shares of common stock (in shares)	80	32
Greater than $11.81
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Average fair value price per share of common stock (in dollars per share)		$ 11.81
Greater than $11.81 | Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Options to purchase shares of common stock (in shares)		371