Marketable securities - Summary of Marketable Securities Held (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Equity securities, amortized cost / cost	$ 20,017	$ 20,017
Marketable securities, amortized cost / cost	915,152	1,488,746
Equity securities, unrealized gains	0	2,150
Marketable securities, unrealized gains	2,838	3,113
Equity securities, unrealized losses	(7,147)	0
Marketable securities, unrealized losses	(7,238)	(3,011)
Equity securities	12,870	22,167
Marketable securities, fair value	910,752	1,488,848
U.S. government agency securities and treasuries
Debt Securities, Available-for-sale [Line Items]
Debt securities, amortized cost / cost	633,970	1,459,649
Debt securities, unrealized gains	2,014	963
Debt securities, unrealized losses	(48)	(3,011)
Debt securities, fair value	635,936	1,457,601
Certificates of deposit
Debt Securities, Available-for-sale [Line Items]
Debt securities, amortized cost / cost	960	9,080
Debt securities, unrealized gains	0	0
Debt securities, unrealized losses	0	0
Debt securities, fair value	960	$ 9,080
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Debt securities, amortized cost / cost	185,827
Debt securities, unrealized gains	824
Debt securities, unrealized losses	(43)
Debt securities, fair value	186,608
Commercial paper
Debt Securities, Available-for-sale [Line Items]
Debt securities, amortized cost / cost	74,378
Debt securities, unrealized gains	0
Debt securities, unrealized losses	0
Debt securities, fair value	$ 74,378

Equity securities unrealized gain.

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Equity securities unrealized loss.

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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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