NET INCOME (LOSS) PER COMMON SHARE - Schedule Of Anti-Dilutive Common Stock Excluded From Computation of Diluted Net Loss Per Share (Detail) - shares shares in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total number of potentially issuable shares (in shares)	8,265	13,394	8,439	20,028
Options to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total number of potentially issuable shares (in shares)	5,172	5,829	5,175	7,388
Common stock issuable under the 2020 notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total number of potentially issuable shares (in shares)	0	3,983	0	3,983
Common stock issuable under the 2024 notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total number of potentially issuable shares (in shares)	0	0	0	3,970
Unvested RSUs
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total number of potentially issuable shares (in shares)	2,900	3,360	3,060	4,029
Common stock potentially issuable for ESPP purchases
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total number of potentially issuable shares (in shares)	193	222	204	453
Common stock held by the NQDC
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total number of potentially issuable shares (in shares)	0	0	0	205