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		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Numerator:
Net loss	$ (712)	$ (8,620)	$ (5,540)	$ (19,636)
Denominator:
Weighted-average common stock outstanding, basic (in shares)	27,634	31,578	29,320	31,335
Dilutive effect of potential common shares, Stock options, restricted stock units, restricted stock awards and employee stock purchase plan (in shares)	0	0	0	0
Dilutive effect of potential common shares, Total shares, diluted (in shares)	27,634	31,578	29,320	31,335
Basic net loss per share (in dollars per share)	$ (0.03)	$ (0.27)	$ (0.19)	$ (0.63)
Diluted net loss per share (in dollars per share)	$ (0.03)	$ (0.27)	$ (0.19)	$ (0.63)