NET INCOME (LOSS) PER SHARE - BASIC AND DILUTED NET INCOME (LOSS) (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Numerator:
Net income (loss)	$ (4,640)	$ (5,287)	$ 57,485	$ (32,997)
Denominator:
Shares used in calculating basic net income (loss) per share (in shares)	30,780,000	29,245,000	30,340,000	29,155,000
Stock options, ESPP, Restricted Stock and RSUs (in shares)	0	0	994,000	0
Shares used in computation of diluted net income (loss) per share (in shares)	30,780,000	29,245,000	31,334,000	29,155,000
Basic net loss per share (in dollars per share)	$ (0.15)	$ (0.18)	$ 1.89	$ (1.13)
Diluted net loss per share (in dollars per share)	$ (0.15)	$ (0.18)	$ 1.83	$ (1.13)
Options to purchase shares of common stock (in shares)			261,667
Average fair value price per share of common stock (in dollars per share)			$ 12.04