Fair value measurements - Recorded Amount of Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Assets:
Restricted cash and cash equivalents	$ 76,683	$ 72,290	$ 130,448	$ 0
Fair value, measurements, recurring
Assets:
Cash and cash equivalents	74,958	71,032
Restricted cash and cash equivalents	1,725	1,258
Restricted investments	32,774	31,768
Total assets	256,304	300,710
Liabilities:
Contingent consideration	2,415	2,180
Total liabilities	2,415	2,180
Fair value, measurements, recurring | U.S. government agency securities and treasuries
Assets:
Marketable securities:	101,625	118,779
Fair value, measurements, recurring | Corporate bonds
Assets:
Marketable securities:		2,498
Fair value, measurements, recurring | Commercial paper
Assets:
Marketable securities:	45,222	75,375
Fair value, measurements, recurring | Quoted prices in active markets (Level 1)
Assets:
Cash and cash equivalents	74,958	71,032
Restricted cash and cash equivalents	1,725	1,258
Restricted investments	0	0
Total assets	76,683	72,290
Liabilities:
Contingent consideration	0	0
Total liabilities	0	0
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
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	0
Restricted cash and cash equivalents	0	0
Restricted investments	32,774	31,768
Total assets	179,621	228,420
Liabilities:
Contingent consideration	0	0
Total liabilities	0	0
Fair value, measurements, recurring | Significant other observable inputs (Level 2) | U.S. government agency securities and treasuries
Assets:
Marketable securities:	101,625	118,779
Fair value, measurements, recurring | Significant other observable inputs (Level 2) | Corporate bonds
Assets:
Marketable securities:		2,498
Fair value, measurements, recurring | Significant other observable inputs (Level 2) | Commercial paper
Assets:
Marketable securities:	45,222	75,375
Fair value, measurements, recurring | Significant unobservable inputs (Level 3)
Assets:
Cash and cash equivalents	0	0
Restricted cash and cash equivalents		0
Restricted investments	0	0
Total assets	0	0
Liabilities:
Contingent consideration	2,415	2,180
Total liabilities	2,415	2,180
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
Fair value, measurements, recurring | Significant unobservable inputs (Level 3) | Commercial paper
Assets:
Marketable securities:	$ 0	$ 0