Income Taxes (Details) - USD ($) |
12 Months Ended | |
|---|---|---|
Dec. 31, 2015 |
Dec. 31, 2014 |
|
| Tax Credit Carryforward [Line Items] | ||
| Increase in valuation allowance | $ 30,600,000 | $ 24,100,000 |
| Tax benefits related to stock-based compensation | 0 | $ 0 |
| Operating loss carryforwards, federal | 250,000,000 | |
| Operating loss carryforwards, state | 155,200,000 | |
| Effective tax rate | 0.00% | |
| Research and Development Tax Credit Carryforward [Member] | Federal [Member] | ||
| Tax Credit Carryforward [Line Items] | ||
| Tax credit carryforwards | 4,500,000 | |
| Research and Development Tax Credit Carryforward [Member] | California [Member] | ||
| Tax Credit Carryforward [Line Items] | ||
| Tax credit carryforwards | $ 5,100,000 | |