NET INCOME (LOSS) PER SHARE - BASIC AND DILUTED NET INCOME (LOSS) (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Numerator:
Net income (loss)	$ 69,883	$ (12,865)
Denominator:
Shares used in calculating basic net income (loss) per share (in shares)	29,700	29,024
Stock options, ESPP, Restricted Stock and RSUs (in shares)	866	0
Shares used in computation of diluted net income (loss) per share (in shares)	30,566	29,024
Basic net loss per share (in dollars per share)	$ 2.35	$ (0.44)
Diluted net loss per share (in dollars per share)	$ 2.29	$ (0.44)
Options to purchase shares of common stock (in shares)	551
Average fair value price per share of common stock (in dollars per share)	$ 10.14