Short-term Investments - Available-for-Sale Securities (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2020	Sep. 30, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Amortized cost		$ 59,329	$ 117,159
Gross unrealized gains		245	147
Gross unrealized losses		0	(2)
Fair value		59,574	117,304
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		59,574	127,822
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized cost		42,865	78,243
Gross unrealized gains		180	89
Gross unrealized losses		0	(2)
Fair value		43,045	78,330
U.S. government-related debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized cost		15,001	26,966
Gross unrealized gains		51	37
Gross unrealized losses		0	0
Fair value		15,052	27,003
Asset-backed Securities
Debt Securities, Available-for-sale [Line Items]
Amortized cost		1,463	11,950
Gross unrealized gains		14	21
Gross unrealized losses		0	0
Fair value		$ 1,477	11,971
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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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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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 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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