Fair value measurements (Details) - USD ($)	Jun. 30, 2021	Dec. 31, 2020
Level 2
Fair value measurements
Assets	$ 0	$ 0
Liabilities	0	0
Level 3
Fair value measurements
Assets	0	0
Liabilities	0	0
Recurring
Fair value measurements
Cash and cash equivalents	6,866,000	9,704,000
Short-term investments	117,000	79,000
Assets	6,983,000	9,783,000
Recurring \| Level 1
Fair value measurements
Cash and cash equivalents	6,866,000	9,704,000
Short-term investments	117,000	79,000
Assets	6,983,000	9,783,000
Non-recurring
Fair value Assumptions
Fair value measurements	$ 0	$ 0

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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

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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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- Definition

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.

+ References

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Fair value of asset after deduction of liability.

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- Definition

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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

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Fair value of financial and nonfinancial obligations.

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