Fair value measurements - Recorded Amount of Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Assets:
Marketable securities:	$ 74,562	$ 235,456
Equity securities	0	3,691
Fair Value, Measurements, Recurring
Assets:
Cash and cash equivalents	66,478	161,160
Equity securities	0	3,691
Total	141,040	396,617
Fair Value, Measurements, Recurring | U.S. government agency securities and treasuries
Assets:
Marketable securities:	68,241	128,393
Fair Value, Measurements, Recurring | Corporate bonds
Assets:
Marketable securities:	6,321	49,308
Fair Value, Measurements, Recurring | Commercial paper
Assets:
Marketable securities:	0	54,065
Fair Value, Measurements, Recurring | Quoted prices in active markets (Level 1)
Assets:
Cash and cash equivalents	66,478	161,146
Equity securities	0	3,691
Total	66,478	164,837
Fair Value, Measurements, Recurring | Quoted prices in active markets (Level 1) | U.S. government agency securities and treasuries
Assets:
Marketable securities:	0	0
Fair Value, Measurements, Recurring | Quoted prices in active markets (Level 1) | Corporate bonds
Assets:
Marketable securities:	0	0
Fair Value, Measurements, Recurring | Quoted prices in active markets (Level 1) | Commercial paper
Assets:
Marketable securities:	0	0
Fair Value, Measurements, Recurring | Significant other observable inputs (Level 2)
Assets:
Cash and cash equivalents	0	14
Equity securities	0	0
Total	74,562	231,780
Fair Value, Measurements, Recurring | Significant other observable inputs (Level 2) | U.S. government agency securities and treasuries
Assets:
Marketable securities:	68,241	128,393
Fair Value, Measurements, Recurring | Significant other observable inputs (Level 2) | Corporate bonds
Assets:
Marketable securities:	6,321	49,308
Fair Value, Measurements, Recurring | Significant other observable inputs (Level 2) | Commercial paper
Assets:
Marketable securities:	0	54,065
Fair Value, Measurements, Recurring | Significant unobservable inputs (Level 3)
Assets:
Cash and cash equivalents	0	0
Equity securities	0	0
Total	0	0
Fair Value, Measurements, Recurring | Significant unobservable inputs (Level 3) | U.S. government agency securities and treasuries
Assets:
Marketable securities:	0	0
Fair Value, Measurements, Recurring | Significant unobservable inputs (Level 3) | Corporate bonds
Assets:
Marketable securities:	0	0
Fair Value, Measurements, Recurring | Significant unobservable inputs (Level 3) | Commercial paper
Assets:
Marketable securities:	$ 0	$ 0