Fair Value Measurements - Schedule of Assets Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Marketable securities	$ 426,710	$ 15,942
Fair Value, Recurring
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Marketable securities		15,942
Restricted cash	1,788	1,774
Total	459,496	17,716
Fair Value, Recurring \| Money Market Fund
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash equivalents	17,208
Fair Value, Recurring \| Corporate Bonds
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash equivalents	13,788
Short-term investments	47,962
Long-term investments	32,768
Fair Value, Recurring \| US Treasuries
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Short-term investments	191,286
Long-term investments	154,696
Fair Value, Recurring \| Level 1
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Marketable securities		15,942
Restricted cash	1,788	1,774
Total	364,978	$ 17,716
Fair Value, Recurring \| Level 1 \| Money Market Fund
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash equivalents	17,208
Fair Value, Recurring \| Level 1 \| US Treasuries
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Short-term investments	191,286
Long-term investments	154,696
Fair Value, Recurring \| Level 2
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total	94,518
Fair Value, Recurring \| Level 2 \| Corporate Bonds
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash equivalents	13,788
Short-term investments	47,962
Long-term investments	$ 32,768

Restricted cash fair value.

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- Definition

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
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Amount of investment in debt and equity securities categorized neither as trading securities nor held-to-maturity securities and intended be sold or mature one year or operating cycle, if longer.

+ References

No definition available.

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- Definition

Amount of 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://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(6))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 1
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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-Section 45
-Paragraph 1
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-URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27161-111563

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- Definition

Investments in debt and equity securities which are categorized neither as held-to-maturity nor trading and which are intended to be sold or mature more than one year from the balance sheet date or operating cycle, if longer. Such securities are reported at fair value; unrealized gains (losses) related to Available-for-sale Securities are excluded from earnings and reported in a separate component of shareholders' equity (other comprehensive income), unless the Available-for-sale security is designated as a hedge or is determined to have had an other than temporary decline in fair value below its amortized cost basis. All or a portion of the unrealized holding gain (loss) of an Available-for-sale security that is designated as being hedged in a fair value hedge is recognized in earnings during the period of the hedge, as are other than temporary declines in fair value below the cost basis for investments in equity securities and debt securities that an entity intends to sell or it is more likely than not that it will be required to sell before the recovery of its amortized cost basis. Other than temporary declines in fair value below the cost basis for debt securities categorized as Available-for-sale that an entity does not intend to sell and for which it is not more likely than not that the entity will be required to sell before the recovery of its amortized cost basis are bifurcated into credit losses and losses related to all other factors. Other than temporary declines in fair value below cost basis related to credit losses are recognized in earnings, and losses related to all other factors are recognized in other comprehensive income.

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- Definition

Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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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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