Basis of Presentation, Summary of Significant Accounting Policies and Recent Accounting Pronouncements - Summary of Fair Value Measurements, Recurring and Nonrecurring (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Assets included in:
Fair value	$ 228,872	$ 36,758
Liabilities included in:
Fair value		5,413
Commercial Paper [Member] | Marketable Debt Securities [Member]
Assets included in:
Fair value	43,923
Corporate Debt Securities [Member] | Marketable Debt Securities [Member]
Assets included in:
Fair value	24,888
Asset-backed Securities [Member] | Marketable Debt Securities [Member]
Assets included in:
Fair value	19,273
US Treasury Securities [Member] | Marketable Debt Securities [Member]
Assets included in:
Fair value	5,988
Preferred stock tranche rights liability [Member]
Liabilities included in:
Fair value		5,033
Preferred stock warrant liability [Member]
Liabilities included in:
Fair value		380
Cash and Cash Equivalents [Member] | Money Market Funds [Member]
Assets included in:
Fair value	134,800	36,758
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets included in:
Fair value	134,800	36,758
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Cash and Cash Equivalents [Member] | Money Market Funds [Member]
Assets included in:
Fair value	134,800	36,758
Significant Other Observable Inputs (Level 2) [Member]
Assets included in:
Fair value	94,072
Significant Other Observable Inputs (Level 2) [Member] | Commercial Paper [Member] | Marketable Debt Securities [Member]
Assets included in:
Fair value	43,923
Significant Other Observable Inputs (Level 2) [Member] | Corporate Debt Securities [Member] | Marketable Debt Securities [Member]
Assets included in:
Fair value	24,888
Significant Other Observable Inputs (Level 2) [Member] | Asset-backed Securities [Member] | Marketable Debt Securities [Member]
Assets included in:
Fair value	19,273
Significant Other Observable Inputs (Level 2) [Member] | US Treasury Securities [Member] | Marketable Debt Securities [Member]
Assets included in:
Fair value	$ 5,988
Significant Unobservable Inputs (Level 3) [Member]
Liabilities included in:
Fair value		5,413
Significant Unobservable Inputs (Level 3) [Member] | Preferred stock tranche rights liability [Member]
Liabilities included in:
Fair value		5,033
Significant Unobservable Inputs (Level 3) [Member] | Preferred stock warrant liability [Member]
Liabilities included in:
Fair value		$ 380