NET INCOME (LOSS) PER SHARE - Reconciliation used in Computing Basic and Diluted Net Income (Loss) per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Numerator:
Net income (loss)	$ 979	$ (1,387)	$ (8,620)	$ (11,016)	$ (3,142)	$ (4,640)	$ (7,758)	$ 69,883	$ (20,044)	$ 54,343	$ (45,291)
Denominator:
Weighted-average common stock outstanding, basic (in shares)	31,731	31,711	31,578	31,089	30,814	30,780	30,527	29,700	31,529	30,459	29,179
Dilutive potential common shares:
Stock options, RSU's, RSAs and ESPP (in shares)									0	948	0
Shares used in computation of diluted net income (loss) per share (in shares)	31,904	31,711	31,578	31,089	30,814	30,780	30,527	30,566	31,529	31,407	29,179
Basic net income (loss) per share (in dollars per share)	$ 0.03	$ (0.04)	$ (0.27)	$ (0.35)	$ (0.10)	$ (0.15)	$ (0.25)	$ 2.35	$ (0.64)	$ 1.78	$ (1.55)
Diluted net income (loss) per share (in dollars per share)	$ 0.03	$ (0.04)	$ (0.27)	$ (0.35)	$ (0.10)	$ (0.15)	$ (0.25)	$ 2.29	$ (0.64)	$ 1.73	$ (1.55)