Quarterly report pursuant to Section 13 or 15(d)

Net Loss Per Share - Warrants, Options and Purchase Rights Excluded from Computation of Diluted Net Loss Per Share (Detail)

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Net Loss Per Share - Warrants, Options and Purchase Rights Excluded from Computation of Diluted Net Loss Per Share (Detail) - shares
shares in Thousands
 3 Months Ended
Mar. 31, 2016
Mar. 31, 2015
Warrants    
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]    
Shares issuable 8,300 12,146
Stock Options    
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]    
Shares issuable 11,561 9,993
2004 Purchase Plan    
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]    
Shares issuable 39 29