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Income Taxes - Additional Information (Detail) - USD ($) | 12 Months Ended |
--- | --- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Income Tax Disclosure [Line Items] |  |  |
Valuation allowance | $ 40,290,000 | $ 26,515,000 | $ 13,060,000
Description of tax benefit likely to be realized upon settlement | greater than 50% |  |
Unrecognized tax benefits | $ 0 |  |
Income tax examination description | In the normal course of business, the Company is subject to examination by federal and state jurisdictions, where applicable. There are currently no pending tax examinations. Tax years from 2015 to the present are open to examination under the statute. |  |
Interest or penalties accrued | $ 0 | 0 |
Income tax cuts and jobs act provisional amounts measurement period | 1 year |  |
Adjustment of deferred tax asset and liabilities due to tax cuts and jobs act | $ 0 |  |
Net impact of revaluation of deferred tax assets and liabilities | 0 |  |
Federal |  |  |
Income Tax Disclosure [Line Items] |  |  |
Net operating loss carryforwards | $ 125,500,000 | $ 82,000,000 |
Net operating loss carryforwards expiration year | 2034 | 2034 |
Federal | Research and Development. |  |  |
Income Tax Disclosure [Line Items] |  |  |
Tax credit carryforwards | $ 2,800,000 |  |
Tax credit carryforwards, expiration year | 2034 |  |
State |  |  |
Income Tax Disclosure [Line Items] |  |  |
Net operating loss carryforwards | $ 125,500,000 | $ 82,000,000 |
Net operating loss carryforwards expiration year | 2034 | 2034 |
State | Research and Development. |  |  |
Income Tax Disclosure [Line Items] |  |  |
Tax credit carryforwards | $ 1,600,000 |  |
Tax credit carryforwards, expiration year | 2029 |  |

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