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Income Taxes - Additional Information (Details) - USD ($) | 12 Months Ended
--- | ---
Dec. 31, 2018 | Dec. 31, 2017
Operating Loss Carryforwards [Line Items] |  |
Income Tax Expense (Benefit) | $ (100,000) | $ 1,700,000
Increase (Decrease) in the valuation allowance | $ 5,800,000 | $ (166,100,000)
Federal statutory income tax rate | 21.00% | 34.00%
Operating Loss Carryforwards Offset of Taxable Income Percentage | 80.00% |
Unrecognized tax benefits that would impact effective tax rate | $ 4,500,000 |
Accrued interest or penalties related to uncertain tax positions | 0 |
Federal Orphan Credit [Member] |  |
Operating Loss Carryforwards [Line Items] |  |
Tax credit carry forward amount | $ 1,200,000 |
Tax credit carryforward expiration year | 2037 |
State [Member] |  |
Operating Loss Carryforwards [Line Items] |  |
Net operating loss carry-forwards | $ 39,100,000 |
Net operating loss carryforwards expiration year | 2033 |
California [Member] | Research and Development [Member] |  |
Operating Loss Carryforwards [Line Items] |  |
Tax credit carry forward amount | $ 19,800,000 |
Federal [Member] |  |
Operating Loss Carryforwards [Line Items] |  |
Net operating loss carry-forwards | $ 48,800,000 |
Net operating loss carryforwards expiration year | 2036 |

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