Anti-Dilutive Common Stock Excluded From Computation of Diluted Net Loss Per Share (Detail) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potential shares of common stock excluded from computation of earnings (loss) per share as they are anti-dilutive	21,999	23,098	25,719
Stock Option
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potential shares of common stock excluded from computation of earnings (loss) per share as they are anti-dilutive	10,323	11,477	13,157
Common stock issuable under the 2017 Notes
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potential shares of common stock excluded from computation of earnings (loss) per share as they are anti-dilutive	1,544	1,992	3,047
Common stock issuable under the 2018 and 2020 Notes
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potential shares of common stock excluded from computation of earnings (loss) per share as they are anti-dilutive	7,966	7,966	7,966
Unvested restricted stock units
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potential shares of common stock excluded from computation of earnings (loss) per share as they are anti-dilutive	1,743	1,244	1,159
Potentially issuable common stock for ESPP purchases
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potential shares of common stock excluded from computation of earnings (loss) per share as they are anti-dilutive	180	195	197
Common stock held by the NQDC
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potential shares of common stock excluded from computation of earnings (loss) per share as they are anti-dilutive	243	224	193