Fair Value Measurements (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Liabilities that are measured at fair value on a recurring basis
Debt securities, fair value	$ 70,094	$ 57,457
Recurring
Liabilities that are measured at fair value on a recurring basis
Assets, fair value	70,094	57,457
Recurring \| Level 1
Liabilities that are measured at fair value on a recurring basis
Assets, fair value	28,059	5,381
Recurring \| Level 2
Liabilities that are measured at fair value on a recurring basis
Assets, fair value	42,035	52,076
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	9,984	11,892
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	9,984	11,892
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	11,186	18,380
Corporate Note Securities \| Recurring \| Level 1
Liabilities that are measured at fair value on a recurring basis
Debt securities, fair value	0	0
Corporate Note Securities \| Recurring \| Level 2
Liabilities that are measured at fair value on a recurring basis
Debt securities, fair value	11,186	18,380
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	13,804	11,295
U.S. government securities \| Recurring
Liabilities that are measured at fair value on a recurring basis
Debt securities, fair value	13,804	11,295
U.S. government securities \| Recurring \| Level 1
Liabilities that are measured at fair value on a recurring basis
Debt securities, fair value	0	0
U.S. government securities \| Recurring \| Level 2
Liabilities that are measured at fair value on a recurring basis
Debt securities, fair value	13,804	11,295
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	3,499
U.S. government agency bonds \| Recurring
Liabilities that are measured at fair value on a recurring basis
Debt securities, fair value	3,499	0
U.S. government agency bonds \| Recurring \| Level 1
Liabilities that are measured at fair value on a recurring basis
Debt securities, fair value	0	0
U.S. government agency bonds \| Recurring \| Level 2
Liabilities that are measured at fair value on a recurring basis
Debt securities, fair value	3,499	0
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	3,562	10,509
Asset-backed Securities \| Recurring
Liabilities that are measured at fair value on a recurring basis
Debt securities, fair value	3,562	10,509
Asset-backed Securities \| Recurring \| Level 1
Liabilities that are measured at fair value on a recurring basis
Debt securities, fair value	0	0
Asset-backed Securities \| Recurring \| Level 2
Liabilities that are measured at fair value on a recurring basis
Debt securities, fair value	3,562	10,509
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	28,059	5,381
Money market funds \| Recurring \| Level 1
Liabilities that are measured at fair value on a recurring basis
Money market funds	28,059	5,381
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
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