Income Taxes - Reconciliation of the Federal Statutory Income Tax Rate to 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%
Permanent items	1.30%	1.60%	5.50%
Excess tax benefit for stock-based compensation	(13.30%)	(2.80%)	(2.00%)
Tax credits	(38.30%)	(3.50%)	(7.20%)
Change in valuation allowance	70.30%	24.50%	(224.10%)
Change in tax rate	0.00%	0.00%	193.80%
Other	1.00%	1.20%	0.00%
(Benefit from) provision for income taxes	0.00%	0.00%	0.00%

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

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Effective income tax rate reconciliation permanent differences.

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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 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 attributable to tax credits. Including, but not limited to, research credit, foreign tax credit, investment tax credit, and other tax credits.

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