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Income Taxes - Additional Information (Details) - USD ($) | 12 Months Ended
--- | ---
Dec. 31, 2018 | Dec. 31, 2017
Income Taxes [Line Items] |  |
Provision or benefit for income taxes | $ 0 | $ 0
Income Tax Contingency [Abstract] |  |
Valuation allowance | 101,091,000 | $ 97,089,000
Increase (decrease) in valuation allowance | $ 4,000,000 |
Corporate income tax rate | 21.00% | 34.00%
Net tax expense related to remeasurement of deferred tax assets and liabilities due to enactment-date effect of act | $ 0 | $ 0
Net operating loss carryforwards, Expire date | begin to expire in 2019 and 2028 |
State tax credit carryforwards | $ 4,500,000 |
Cumulative change in ownership | 50.00% |
Period of net operating loss and R&D tax credit carry forwards to offset future taxable income | 3 years |
Provisional amount of remeasured deferred tax assets and liabilities due to change in tax rate fully offset by valuation allowance |  | 45,800,000
Liability for uncertain tax positions | $ 0 | $ 0
Period for material changes of liability for uncertain tax benefits | 12 months |
Interest related to unrecognized tax benefits in interest expense and penalties | $ 0 |
Maximum [Member] |  |
Income Tax Contingency [Abstract] |  |
Corporate income tax rate |  | 35.00%
Federal [Member] |  |
Income Tax Contingency [Abstract] |  |
Tax loss carryforwards | 380,600,000 |
Federal tax carry forward | $ 5,200,000 |
Federal tax credit carryforward, Expiration date | begin to expire in 2019 |
Net operating losses | $ 13,100,000 |
Federal [Member] | Maximum [Member] |  |
Income Tax Contingency [Abstract] |  |
Percentage of federal net operating losses used to offset of future taxable income | 80.00% |
State [Member] |  |
Income Tax Contingency [Abstract] |  |
Tax loss carryforwards | $ 156,800,000 |

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