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Balance Sheet Account Details - Investment Categories (Details) - USD ($) $ in Thousands | Dec. 31, 2020 | Dec. 31, 2019
--- | --- | ---
Short-term investments |  |
Debt Securities, Available-for-sale [Line Items] |  |
Cost | $ 324,567 | $ 941,175
Gross unrealized gains | 1,302 | 933
Gross unrealized losses | (1,391) | (2,118)
Estimated fair value | 324,478 | 939,990
Mutual fund |  |
Debt Securities, Available-for-sale [Line Items] |  |
Cost | 151,512 | 250,636
Gross unrealized gains | 386 | 0
Gross unrealized losses | 0 | (249)
Estimated fair value | 151,898 | 250,387
Bank deposits |  |
Debt Securities, Available-for-sale [Line Items] |  |
Cost | 84,120 | 411,690
Gross unrealized gains | 35 | 188
Gross unrealized losses | (1) | (3)
Estimated fair value | 84,154 | 411,875
Commercial paper |  |
Debt Securities, Available-for-sale [Line Items] |  |
Cost | 45,459 | 210,525
Gross unrealized gains | 27 | 43
Gross unrealized losses | (1) | (16)
Estimated fair value | 45,485 | 210,552
Corporate bonds |  |
Debt Securities, Available-for-sale [Line Items] |  |
Cost | 30,512 | 63,818
Gross unrealized gains | 99 | 161
Gross unrealized losses | (1) | 0
Estimated fair value | 30,610 | 63,979
Agency bonds |  |
Debt Securities, Available-for-sale [Line Items] |  |
Cost | 4,499 |
Gross unrealized gains | 2 |
Gross unrealized losses | 0 |
Estimated fair value | 4,501 |
Corporate equity securities |  |
Debt Securities, Available-for-sale [Line Items] |  |
Cost | 4,466 | 4,506
Gross unrealized gains | 360 | 416
Gross unrealized losses | (1,388) | (1,850)
Estimated fair value | 3,438 | 3,072
Treasury bill |  |
Debt Securities, Available-for-sale [Line Items] |  |
Cost | 3,999 |
Gross unrealized gains | 0 |
Gross unrealized losses | 0 |
Estimated fair value | 3,999 |
Warrants |  |
Debt Securities, Available-for-sale [Line Items] |  |
Cost | 0 | 0
Gross unrealized gains | 393 | 125
Gross unrealized losses | 0 | 0
Estimated fair value | $ 393 | $ 125

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- Definition 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). + 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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