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Income Taxes - Reconciliation of Total Income Tax Provision (Details) | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2017
Reconciliation of the total income tax provision tax rate [Abstract] |  |
Income tax expense (benefit) at federal statutory rate | (21.00%) | (34.00%)
Income tax expense (benefit) at state statutory rate | (8.20%) | (6.70%)
Change in valuation allowance | 35.80% | (324.50%)
Change in state rate | (0.10%) | (1.50%)
Permanent interest adjustments | 0.70% | 0.40%
Stock compensation | 1.80% | 5.20%
Research credit | (1.40%) | (1.90%)
Foreign rate differential |  | 350.40%
NOLs expiring and adjustments to NOL |  | 12.10%
Mark to market adjustment | (5.30%) |
Other, net | (2.30%) | 0.50%
Total income tax provision | 0.00% | 0.00%

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- Definition Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to net operating loss expiration. + References No definition available. + Details
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