Income Taxes - Schedule of Reconciliation of the Federal Statutory Income Tax Rate and the Company's Effective Income Tax Rate (Detail)	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Federal statutory income tax rate	(21.00%)	(21.00%)	(34.00%)
State income taxes	(8.90%)	(8.60%)	(6.90%)
Research and development tax credits	(5.10%)	(4.70%)	(3.40%)
Stock-based compensation	1.20%	(0.60%)	3.60%
Change in U.S. tax rate			18.70%
Change in valuation allowance	33.80%	34.90%	22.00%

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 difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying domestic federal statutory income tax rate to pretax income (loss) from continuing operation, attributable to nondeductible expense for share-based payment arrangement.

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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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