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Balance Sheet Components - Summary of Amortized Cost, Gross Unrealized Holding Gains or Losses, and Fair Value of Available-for-Sale Investments (Detail) - USD ($) $ in Thousands | Jun. 30, 2020 | Dec. 31, 2019
--- | --- | ---
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | $ 255,242 | $ 467,850
Gross Unrealized Holding Gains | 1,304 | 784
Gross Unrealized Holding Losses | 0 | (25)
Fair Value | 256,546 | 468,609
U.S. treasury notes and bills [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | 225,117 | 426,995
Gross Unrealized Holding Gains | 1,062 | 536
Gross Unrealized Holding Losses | 0 | (25)
Fair Value | 226,179 | 427,506
Certificate of deposit [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | 30,000 | 30,000
Gross Unrealized Holding Gains | 138 | 32
Gross Unrealized Holding Losses | 0 | 0
Fair Value | 30,138 | 30,032
Bond and mutual funds [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost |  | 10,730
Gross Unrealized Holding Gains |  | 86
Gross Unrealized Holding Losses |  | 0
Fair Value |  | 10,816
Equity investments [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | 125 | 125
Gross Unrealized Holding Gains | 104 | 130
Gross Unrealized Holding Losses | 0 | 0
Fair Value | $ 229 | $ 255

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- Definition Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27161-111563 + Details
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