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		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Numerator:
Net income (loss)	$ 2,855	$ (1,387)	$ (2,685)	$ (21,023)
Denominator:
Weighted-average common stock outstanding, basic (in shares)	26,898	31,711	28,507	31,461
Dilutive effect of potential common shares, Stock options, restricted stock units, restricted stock awards and employee stock purchase plan (in shares)	236	0	0	0
Dilutive effect of potential common shares, Total shares, diluted (in shares)	27,134	31,711	28,507	31,461
Basic net loss per share (in dollars per share)	$ 0.11	$ (0.04)	$ (0.09)	$ (0.67)
Diluted net loss per share (in dollars per share)	$ 0.11	$ (0.04)	$ (0.09)	$ (0.67)