Summary of Significant Accounting Policies - Anti-Dilutive Securities Excluded from the Computation of Diluted Net Loss per Share (Detail) - shares shares in Thousands |
3 Months Ended | |
|---|---|---|
Mar. 31, 2019 |
Mar. 31, 2018 |
|
| Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] | ||
| Anti-dilutive securities excluded from the computation of diluted loss per share | 7,476 | 6,285 |
| Common Stock Options [Member] | ||
| Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] | ||
| Anti-dilutive securities excluded from the computation of diluted loss per share | 7,349 | 5,173 |
| Incentive Awards [Member] | ||
| Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] | ||
| Anti-dilutive securities excluded from the computation of diluted loss per share | 127 | 130 |
| Common Stock Warrants [Member] | ||
| Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] | ||
| Anti-dilutive securities excluded from the computation of diluted loss per share | 982 | |