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Financial Instruments - Fair value hierarchy (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Financial Instruments Measurements
Transfers between fair value measurement levels	$ 0	$ 0	$ 0	$ 0
Reverse repurchase agreements | Government Securities and Obligations
Financial Instruments Measurements
Percentage of investment amount to collateralized deposits value			102.00%
Recurring
Assets:
Total	72,876		$ 72,876		$ 207,856
Recurring | Level 1
Assets:
Total	3,876		3,876		7,924
Recurring | Level 2
Assets:
Total	69,000		69,000		199,932
Recurring | Money market funds
Assets:
Cash and cash equivalents:	3,876		3,876		1,944
Recurring | Money market funds | Level 1
Assets:
Cash and cash equivalents:	3,876		3,876		1,944
Recurring | Corporate debt securities
Assets:
Short-term investments:					16,445
Recurring | Corporate debt securities | Level 2
Assets:
Short-term investments:					16,445
Recurring | Yankee securities
Assets:
Short-term investments:					1,999
Recurring | Yankee securities | Level 2
Assets:
Short-term investments:					1,999
Recurring | Bonds
Assets:
Short-term investments:					2,988
Recurring | Bonds | Level 2
Assets:
Short-term investments:					2,988
Recurring | Treasury bills
Assets:
Short-term investments:					5,980
Recurring | Treasury bills | Level 1
Assets:
Short-term investments:					5,980
Recurring | Reverse repurchase agreements
Assets:
Short-term investments:	69,000		69,000		178,500
Recurring | Reverse repurchase agreements | Level 2
Assets:
Short-term investments:	$ 69,000		$ 69,000		$ 178,500

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- Definition

The percentage of investment in reverse repurchase agreements which are collateralized by deposits.

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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
-Name Accounting Standards Codification
-Topic 820
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-Section 50
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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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+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
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-Section 50
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Amount of transfer of financial instrument classified as an asset into (out of) level 3 of the fair value hierarchy.

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Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

+ References

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