NET INCOME (LOSS) PER SHARE - RECONCILIATION OF NUMERATORS AND DENOMINATORS USED IN COMPUTING BASIC AND DILUTED NET INCOME (LOSS) PER SHARE (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Numerator:
Net loss	$ (4,828)	$ (11,016)
Denominator:
Weighted-average common stock outstanding, basic (in shares)	31,006	31,089
Dilutive effect of potential common shares, Stock options, restricted stock units, restricted stock awards and employee stock purchase plan (in shares)	0	0
Dilutive effect of potential common shares, Total shares, diluted (in shares)	31,006	31,089
Basic net loss per share (in dollars per share)	$ (0.16)	$ (0.35)
Diluted net loss per share (in dollars per share)	$ (0.16)	$ (0.35)