Fair value measurements - Recorded Amount of Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Assets:
Equity securities	$ 5,653	$ 12,870
U.S. government agency securities and treasuries
Assets:
Marketable securities	675,271	635,936
Certificates of deposit
Assets:
Marketable securities		960
Corporate bonds
Assets:
Marketable securities	197,563	186,608
Commercial paper
Assets:
Marketable securities	77,950	74,378
Fair value, measurements, recurring
Assets:
Cash and cash equivalents	317,705	327,214
Equity securities	5,653	12,870
Total assets	1,274,142	1,237,966
Liabilities:
Contingent consideration	1,509	7,977
Total liabilities	1,509	7,977
Fair value, measurements, recurring \| U.S. government agency securities and treasuries
Assets:
Marketable securities	675,271
Fair value, measurements, recurring \| U.S. government agency securities and treasuries
Assets:
Marketable securities		635,936
Fair value, measurements, recurring \| Certificates of deposit
Assets:
Marketable securities		960
Fair value, measurements, recurring \| Corporate bonds
Assets:
Marketable securities	197,563	186,608
Fair value, measurements, recurring \| Commercial paper
Assets:
Marketable securities	77,950	74,378
Fair value, measurements, recurring \| Quoted prices in active markets (Level 1)
Assets:
Cash and cash equivalents	317,705	311,245
Equity securities	5,653	12,870
Total assets	323,358	324,115
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
Fair value, measurements, recurring \| Quoted prices in active markets (Level 1) \| U.S. government agency securities and treasuries
Assets:
Marketable securities		0
Fair value, measurements, recurring \| Quoted prices in active markets (Level 1) \| Certificates of deposit
Assets:
Marketable securities		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	15,969
Equity securities	0	0
Total assets	950,784	913,851
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	675,271
Fair value, measurements, recurring \| Significant other observable inputs (Level 2) \| U.S. government agency securities and treasuries
Assets:
Marketable securities		635,936
Fair value, measurements, recurring \| Significant other observable inputs (Level 2) \| Certificates of deposit
Assets:
Marketable securities		960
Fair value, measurements, recurring \| Significant other observable inputs (Level 2) \| Corporate bonds
Assets:
Marketable securities	197,563	186,608
Fair value, measurements, recurring \| Significant other observable inputs (Level 2) \| Commercial paper
Assets:
Marketable securities	77,950	74,378
Fair value, measurements, recurring \| Significant unobservable inputs (Level 3)
Assets:
Cash and cash equivalents	0	0
Equity securities	0	0
Total assets	0	0
Liabilities:
Contingent consideration	1,509	7,977
Total liabilities	1,509	7,977
Fair value, measurements, recurring \| Significant unobservable inputs (Level 3) \| U.S. government agency securities and treasuries
Assets:
Marketable securities	0
Fair value, measurements, recurring \| Significant unobservable inputs (Level 3) \| U.S. government agency securities and treasuries
Assets:
Marketable securities		0
Fair value, measurements, recurring \| Significant unobservable inputs (Level 3) \| Certificates of deposit
Assets:
Marketable securities		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

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of liability recognized arising from contingent consideration in a business combination, expected to be settled beyond one year or the normal operating cycle, if longer.

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Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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Fair value of financial and nonfinancial obligations.

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