Fair Value Measurements - Schedule of Fair Value Measurements of Cash Equivalents (Detail) - USD ($)	Sep. 30, 2024	Dec. 31, 2023
Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities	$ 0	$ 0
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities	790,645,000	423,372,000
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities	225,099,000	10,698,000
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities	565,546,000	412,674,000
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities	0	0
Fair Value, Measurements, Recurring | Money Market Funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities	225,099,000	10,698,000
Fair Value, Measurements, Recurring | Money Market Funds | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities	225,099,000	10,698,000
Fair Value, Measurements, Recurring | Money Market Funds | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities	0	0
Fair Value, Measurements, Recurring | Money Market Funds | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities	0	0
Fair Value, Measurements, Recurring | U.S. Government Agency Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities	135,946,000	150,595,000
Fair Value, Measurements, Recurring | U.S. Government Agency Securities | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities	0	0
Fair Value, Measurements, Recurring | U.S. Government Agency Securities | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities	135,946,000	150,595,000
Fair Value, Measurements, Recurring | U.S. Government Agency Securities | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities	0	0
Fair Value, Measurements, Recurring | FDIC Certificates of Deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities	980,000	4,400,000
Fair Value, Measurements, Recurring | FDIC Certificates of Deposit | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities	0	0
Fair Value, Measurements, Recurring | FDIC Certificates of Deposit | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities	980,000	4,400,000
Fair Value, Measurements, Recurring | FDIC Certificates of Deposit | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities	0	0
Fair Value, Measurements, Recurring | Certificates of Deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities	60,000,000	60,000,000
Fair Value, Measurements, Recurring | Certificates of Deposit | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities	0	0
Fair Value, Measurements, Recurring | Certificates of Deposit | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities	60,000,000	60,000,000
Fair Value, Measurements, Recurring | Certificates of Deposit | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities	0	0
Fair Value, Measurements, Recurring | Commercial Paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities	51,699,000	78,642,000
Fair Value, Measurements, Recurring | Commercial Paper | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities	0	0
Fair Value, Measurements, Recurring | Commercial Paper | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities	51,699,000	78,642,000
Fair Value, Measurements, Recurring | Commercial Paper | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities	0	0
Fair Value, Measurements, Recurring | Corporate Notes/Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities	316,921,000	119,037,000
Fair Value, Measurements, Recurring | Corporate Notes/Bonds | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities	0	0
Fair Value, Measurements, Recurring | Corporate Notes/Bonds | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities	316,921,000	119,037,000
Fair Value, Measurements, Recurring | Corporate Notes/Bonds | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities	$ 0	$ 0