Marketable Securities - Summary of Marketable Securities Held (Detail) - USD ($)	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Equity Securities, Amortized cost / Cost	$ 20,017,000	$ 20,017,000
Equity Securities, Unrealized gains	0	0
Equity Securities, Unrealized losses	(11,667,000)	(7,147,000)
Equity securities	8,350,000	12,870,000
Marketable Securities, Amortized cost / Cost	681,166,000	915,152,000
Marketable Securities, Unrealized gains	3,354,000	2,838,000
Marketable Securities, Unrealized losses	(12,792,000)	(7,238,000)
Marketable securities:	671,728,000	910,752,000
Debt securities, available-for-sale, noncurrent	0		$ 0
U.S. government agency securities and treasuries
Debt Securities, Available-for-sale [Line Items]
Debt Securities. Amortized cost / Cost	377,551,000	633,970,000
Debt Securities, Unrealized gains	2,741,000	2,014,000
Debt Securities, Unrealized losses	(15,000)	(48,000)
Debt Securities, Fair value	380,277,000	635,936,000
Certificates of deposit
Debt Securities, Available-for-sale [Line Items]
Debt Securities. Amortized cost / Cost	240,000	960,000
Debt Securities, Unrealized gains	0	0
Debt Securities, Unrealized losses	0	0
Debt Securities, Fair value	240,000	960,000
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Debt Securities. Amortized cost / Cost	207,708,000	185,827,000
Debt Securities, Unrealized gains	613,000	824,000
Debt Securities, Unrealized losses	(1,110,000)	(43,000)
Debt Securities, Fair value	207,211,000	186,608,000
Commercial paper
Debt Securities, Available-for-sale [Line Items]
Debt Securities. Amortized cost / Cost	75,650,000	74,378,000
Debt Securities, Unrealized gains	0	0
Debt Securities, Unrealized losses	0	0
Debt Securities, Fair value	$ 75,650,000	$ 74,378,000

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 debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), classified as noncurrent.

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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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