Federal Income Tax Provision Compared With Statutory Rates (Detail) |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2016 |
Dec. 31, 2015 |
Dec. 31, 2014 |
|
| Income Tax Disclosure [Abstract] | |||
| Statutory regular federal income tax rate | (34.00%) | (34.00%) | (34.00%) |
| Change in valuation allowance | 40.40% | 40.20% | 37.40% |
| State tax benefit (net of federal benefit) | (3.00%) | (3.10%) | (3.30%) |
| Research credits | (3.40%) | (3.10%) | (1.90%) |
| Foreign amounts with no tax benefit | 0.20% | 0.10% | (0.10%) |
| Non-deductible expenses | 0.60% | 0.40% | 1.00% |
| Effect of change in rate | 0.50% | 0.90% | 2.30% |
| Other | (0.20%) | (0.50%) | (0.80%) |
| Total | 1.10% | 0.90% | 0.60% |