NET INCOME (LOSS) PER SHARE - Tabular Disclosure (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Basic
Net income (loss)	$ 6,842	$ 4,538	$ (8,323)	$ (844)	$ (10,466)	$ (16,834)	$ 3,057	$ (28,144)
Undistributed earnings allocated to participating securities	(221)			0			(92)	0
Net income (loss) attributable to common stockholders—basic	$ 6,621			$ (844)			$ 2,965	$ (28,144)
Weighted average shares used in computing net income (loss) per share attributable to common stockholders - basic (in shares)	148,456			147,339			148,124	144,662
Net (loss) income per share attributable to common stockholders - basic (in dollars per share)	$ 0.04			$ (0.01)			$ 0.02	$ (0.19)
Diluted
Net income (loss) attributable to common stockholders—diluted	$ 6,621			$ (844)			$ 2,965	$ (28,144)
Effect of dilutive securities (in shares)	341			0			349	0
Weighted average shares used in computing net income (loss) per share attributable to common stockholders - diluted (in shares)	148,797			147,339			148,473	144,662
Net income (loss) per share attributable to common stockholders - diluted (in dollars per share)	$ 0.04			$ (0.01)			$ 0.02	$ (0.19)