Financial Instruments - Fair Value Measured On A Recurring Basis (Detail) - USD ($)	Sep. 30, 2023	Dec. 31, 2022
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Short-term investments	$ 44,792,000	$ 57,534,000
Long-term investments	18,137,000	41,978,000
Assets measured at fair value	313,913,000	328,641,000
Level 1
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Assets measured at fair value	262,143,000	249,139,000
Level 2
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Assets measured at fair value	51,770,000	79,502,000
U.S. government agency bonds | Fair Value, Measurements, Recurring | Short-term investments:
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Short-term investments	4,188,000
U.S. government agency bonds | Fair Value, Measurements, Recurring | Level 1 | Short-term investments:
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Short-term investments	0
U.S. government agency bonds | Fair Value, Measurements, Recurring | Level 2 | Short-term investments:
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Short-term investments	4,188,000
U.S. government treasury bonds | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Short-term investments	6,503,000	15,404,000
Long-term investments	4,656,000	4,606,000
U.S. government treasury bonds | Fair Value, Measurements, Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Short-term investments	6,503,000	15,404,000
Long-term investments	4,656,000	4,606,000
U.S. government treasury bonds | Fair Value, Measurements, Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Short-term investments	0	0
Long-term investments	0	0
Corporate bonds | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Short-term investments	31,828,000	36,510,000
Long-term investments	11,584,000	29,965,000
Corporate bonds | Fair Value, Measurements, Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Short-term investments	0	0
Long-term investments	0	0
Corporate bonds | Fair Value, Measurements, Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Short-term investments	31,828,000	36,510,000
Long-term investments	11,584,000	29,965,000
Municipal bonds | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Short-term investments	691,000	2,711,000
Long-term investments		675,000
Municipal bonds | Fair Value, Measurements, Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Short-term investments	0	0
Long-term investments		0
Municipal bonds | Fair Value, Measurements, Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Short-term investments	691,000	2,711,000
Long-term investments		675,000
U.S. government agency bonds | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Long-term investments	1,009,000	5,163,000
U.S. government agency bonds | Fair Value, Measurements, Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Long-term investments	0	0
U.S. government agency bonds | Fair Value, Measurements, Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Long-term investments	1,009,000	5,163,000
Asset-backed securities | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Short-term investments	1,582,000	2,909,000
Long-term investments	888,000	1,569,000
Asset-backed securities | Fair Value, Measurements, Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Short-term investments	0	0
Long-term investments	0	0
Asset-backed securities | Fair Value, Measurements, Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Short-term investments	1,582,000	2,909,000
Long-term investments	888,000	1,569,000
Money market funds | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Cash equivalents	250,984,000	229,129,000
Money market funds | Fair Value, Measurements, Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Cash equivalents	250,984,000	229,129,000
Money market funds | Fair Value, Measurements, Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Cash equivalents	$ 0	$ 0