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 6 Months Ended
Jun. 30, 2016
Jun. 30, 2015
Jun. 30, 2016
Jun. 30, 2015
Warrants        
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]        
Shares issuable 8,300 8,300 8,300 12,146
Stock Options        
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]        
Shares issuable 11,635 10,151 11,635 10,151
2004 Purchase Plan        
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]        
Shares issuable 42 73 42 73