(LOSS) PER SHARE (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019	Feb. 29, 2020
Earning per share reconciliation
Net (loss)	$ (19,267)	$ (20,740)	$ (25,372)	$ (30,338)	$ (32,296)	$ (28,717)	$ (65,379)	$ (91,351)
Weighted-average common shares outstanding (in shares)	80,537			79,200			80,191	78,928
(Loss) per share, basic (in dollars per share)	$ (0.24)			$ (0.38)			$ (0.82)	$ (1.16)
Weighted-average common shares outstanding, assuming dilution (in shares)	80,537			79,200			80,191	78,928
(Loss) per share, diluted (in dollars per share)	$ (0.24)			$ (0.38)			$ (0.82)	$ (1.16)
Outstanding anti-dilutive stock options and RSUs (in shares)	6,622			5,953			6,166	5,923
Convertible debt
Earning per share reconciliation
Initial conversion price (in dollars per share)									$ 135.05