Fair Value Measurements (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Liabilities that are measured at fair value on a recurring basis
Debt securities, fair value	$ 70,020	$ 69,984
Recurring
Liabilities that are measured at fair value on a recurring basis
Assets, fair value	70,020	69,984
Recurring \| Level 1
Liabilities that are measured at fair value on a recurring basis
Assets, fair value	15,598	3,698
Recurring \| Level 2
Liabilities that are measured at fair value on a recurring basis
Assets, fair value	54,422	66,286
Recurring \| Level 3
Liabilities that are measured at fair value on a recurring basis
Assets, fair value	0	0
Commercial paper \| Recurring
Liabilities that are measured at fair value on a recurring basis
Debt securities, fair value	9,998	8,994
Commercial paper \| Recurring \| Level 1
Liabilities that are measured at fair value on a recurring basis
Debt securities, fair value	0	0
Commercial paper \| Recurring \| Level 2
Liabilities that are measured at fair value on a recurring basis
Debt securities, fair value	9,998	8,994
Commercial paper \| Recurring \| Level 3
Liabilities that are measured at fair value on a recurring basis
Debt securities, fair value	0	0
Corporate Note Securities \| Recurring
Liabilities that are measured at fair value on a recurring basis
Debt securities, fair value	40,035	35,911
Corporate Note Securities \| Recurring \| Level 1
Liabilities that are measured at fair value on a recurring basis
Debt securities, fair value	0
Corporate Note Securities \| Recurring \| Level 2
Liabilities that are measured at fair value on a recurring basis
Debt securities, fair value	40,035	35,911
Corporate Note Securities \| Recurring \| Level 3
Liabilities that are measured at fair value on a recurring basis
Debt securities, fair value	0	0
U.S. government securities
Liabilities that are measured at fair value on a recurring basis
Debt securities, fair value	1,500	12,842
U.S. government securities \| Recurring
Liabilities that are measured at fair value on a recurring basis
Debt securities, fair value	1,500	12,842
U.S. government securities \| Recurring \| Level 1
Liabilities that are measured at fair value on a recurring basis
Debt securities, fair value	0
U.S. government securities \| Recurring \| Level 2
Liabilities that are measured at fair value on a recurring basis
Debt securities, fair value	1,500	12,842
U.S. government securities \| Recurring \| Level 3
Liabilities that are measured at fair value on a recurring basis
Debt securities, fair value	0	0
U.S. government agency bonds
Liabilities that are measured at fair value on a recurring basis
Debt securities, fair value	1,074	5,001
U.S. government agency bonds \| Recurring
Liabilities that are measured at fair value on a recurring basis
Debt securities, fair value	1,074	5,001
U.S. government agency bonds \| Recurring \| Level 1
Liabilities that are measured at fair value on a recurring basis
Debt securities, fair value	0
U.S. government agency bonds \| Recurring \| Level 2
Liabilities that are measured at fair value on a recurring basis
Debt securities, fair value	1,074	5,001
U.S. government agency bonds \| Recurring \| Level 3
Liabilities that are measured at fair value on a recurring basis
Debt securities, fair value	0	0
Asset-backed Securities
Liabilities that are measured at fair value on a recurring basis
Debt securities, fair value	1,815	3,538
Asset-backed Securities \| Recurring
Liabilities that are measured at fair value on a recurring basis
Debt securities, fair value	1,815	3,538
Asset-backed Securities \| Recurring \| Level 1
Liabilities that are measured at fair value on a recurring basis
Debt securities, fair value	0
Asset-backed Securities \| Recurring \| Level 2
Liabilities that are measured at fair value on a recurring basis
Debt securities, fair value	1,815	3,538
Asset-backed Securities \| Recurring \| Level 3
Liabilities that are measured at fair value on a recurring basis
Debt securities, fair value	0	0
Money market funds \| Recurring
Liabilities that are measured at fair value on a recurring basis
Money market funds	15,598	3,698
Money market funds \| Recurring \| Level 1
Liabilities that are measured at fair value on a recurring basis
Money market funds	15,598	3,698
Money market funds \| Recurring \| Level 2
Liabilities that are measured at fair value on a recurring basis
Money market funds	0	0
Money market funds \| Recurring \| Level 3
Liabilities that are measured at fair value on a recurring basis
Money market funds	$ 0	$ 0

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

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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).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
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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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