Stockholders' Equity (Common Stock Reserved for Future Issuance) (Detail) shares in Thousands	Mar. 31, 2020 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock options outstanding (in shares)	6,116
Total common shares reserved for future issuance (in shares)	85,216
Common stock available for future grant under 2019 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock available for future grant (in shares)	1,571
Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock available for future grant (in shares)	190
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
RSUs outstanding (in shares)	89
Class A-1 Convertible Preferred Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Preferred stock, shares outstanding (in shares)	4,159
Class A-2 Convertible Preferred Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Preferred stock, shares outstanding (in shares)	26,317
Initial Closing Warrants
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Warrants outstanding (in shares)	13,890
Milestone Closing Warrants
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Warrants outstanding (in shares)	32,884

Number of warrants or rights outstanding.

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Aggregate number of common shares reserved for future issuance.

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