Short-term Investments - Available-for-Sale Securities (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Amortized cost	$ 117,159	$ 69,681
Gross unrealized gains	147	1
Gross unrealized losses	(2)	(41)
Fair value	117,304	69,641
Debt securities and equity securities, amortized cost	127,052
Debt securities and equity securities, unrealized gains	772
Debt securities and equity securities, unrealized losses	(2)
Short-term investments	127,822
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized cost	78,243	47,299
Gross unrealized gains	89	1
Gross unrealized losses	(2)	(21)
Fair value	78,330	47,279
U.S. government-related debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized cost	26,966	14,972
Gross unrealized gains	37	0
Gross unrealized losses	0	(11)
Fair value	27,003	14,961
Asset-backed Securities
Debt Securities, Available-for-sale [Line Items]
Amortized cost	11,950	7,410
Gross unrealized gains	21	0
Gross unrealized losses	0	(9)
Fair value	11,971	$ 7,401
Corporate equity securities
Debt Securities, Available-for-sale [Line Items]
Equity securities, amortized cost	9,893
Equity securities, unrealized gain	625
Equity securities, unrealized loss	0
Equity securities, fair value	$ 10,518

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Debt Securities And Equity Securities, Fair Value

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Debt Securities And Equity Securities, Unrealized Gains

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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), classified as current.

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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 unrealized gain on investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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

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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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