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, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Numerator:
Net income (loss)	$ 5,341	$ (712)	$ 7,377	$ (5,540)
Denominator:
Weighted-average common stock outstanding, basic (in shares)	30,982	27,634	29,787	29,320
Dilutive effect of potential common shares, Stock options, restricted stock units, restricted stock awards and employee stock purchase plan (in shares)	265	0	466	0
Dilutive effect of potential common shares, Total shares, diluted (in shares)	31,247	27,634	30,253	29,320
Basic net loss per share (in dollars per share)	$ 0.17	$ (0.03)	$ 0.25	$ (0.19)
Diluted net loss per share (in dollars per share)	$ 0.17	$ (0.03)	$ 0.24	$ (0.19)