Income Taxes - Schedule of Reconciliation of Income Tax Expense (Benefit) (Detail)	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Federal income tax expense at statutory rate	21.00%	34.00%
State income taxes, net of federal benefit	5.20%	4.90%
Permanent differences	(0.80%)	(0.30%)
U.S.-TCJA		(14.80%)
Foreign rate differential	0.20%	(0.20%)
Research and development tax credits	1.10%	1.30%
Change in valuation allowance	(26.50%)	(24.90%)
Provision to Return	(0.20%)
Effective income tax rate	0.00%	0.00%

Effective income tax rate reconciliation permanent difference.

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Effective income tax rate reconciliation Tax Cuts And Jobs Act 2017 percent.

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Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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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 changes in the valuation allowance for deferred tax assets.

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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 applicable to statutory income tax expense (benefit) outside of the country of domicile.

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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 revisions of previously reported income tax expense.

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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 applicable to state and local income tax expense (benefit), net of federal tax expense (benefit).

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