Marketable securities - Summary of Marketable Securities Held (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Equity securities, amortized cost / cost	$ 20,017	$ 20,017
Marketable securities, amortized cost / cost	970,180	915,152
Equity securities, unrealized gains	0	0
Marketable securities, unrealized gains	735	2,838
Equity securities, unrealized losses	(14,364)	(7,147)
Marketable securities, unrealized losses	(14,478)	(7,238)
Equity securities	5,653	12,870
Marketable securities, fair value	956,437	910,752
U.S. government agency securities and treasuries
Debt Securities, Available-for-sale [Line Items]
Debt securities, amortized cost / cost	675,043	633,970
Debt securities, unrealized gains	302	2,014
Debt securities, unrealized losses	(74)	(48)
Debt securities, fair value	675,271	635,936
Certificates of deposit
Debt Securities, Available-for-sale [Line Items]
Debt securities, amortized cost / cost		960
Debt securities, unrealized gains		0
Debt securities, unrealized losses		0
Debt securities, fair value		960
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Debt securities, amortized cost / cost	197,171	185,827
Debt securities, unrealized gains	432	824
Debt securities, unrealized losses	(40)	(43)
Debt securities, fair value	197,563	186,608
Commercial paper
Debt Securities, Available-for-sale [Line Items]
Debt securities, amortized cost / cost	77,949	74,378
Debt securities, unrealized gains	1	0
Debt securities, unrealized losses	0	0
Debt securities, fair value	$ 77,950	$ 74,378

Equity securities unrealized gain.

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Equity securities unrealized loss.

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- Definition

Marketable securities amortized cost.

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Marketable securities unrealized gains.

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Marketable securities unrealized loss.

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Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on 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, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on 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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Amortized cost 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 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 investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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Cost of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI). Excludes equity method investment and investment in equity security without readily determinable fair value.

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Amount of investment in marketable security.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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