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Fair value measurements (Details 3) - USD ($) $ in Thousands | Dec. 31, 2022 | Dec. 31, 2021
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Concentration risks, percentage [Abstract] |  |
Percentage in fixed-income investments | 63.00% | 61.00%
Percentage investment in common stock of large-cap companies | 15.00% | 17.00%
Percentage investment in common stock of mid-cap companies | 8.00% | 8.00%
Percentage investment in common stock of small-cap companies | 6.00% | 7.00%
Percentage investment in target date investments | 6.00% | 5.00%
Percentage investment in cash and cash equivalents | 2.00% | 2.00%
Fair value, measurements, recurring |  |
Fair value measurements [Line Items] |  |
Assets, fair value disclosure | $ 116,232 | $ 130,895
Fair value, measurements, recurring | Money market funds |  |
Fair value measurements [Line Items] |  |
Assets, fair value disclosure | 7,361 | 10,190
Fair value, measurements, recurring | Insurance contracts* |  |
Fair value measurements [Line Items] |  |
Assets, fair value disclosure | 98,041 | 109,603
Fair value, measurements, recurring | Mortgage-backed securities |  |
Fair value measurements [Line Items] |  |
Assets, fair value disclosure | 8,294 | 8,706
Fair value, measurements, recurring | U.S. Treasury securities |  |
Fair value measurements [Line Items] |  |
Assets, fair value disclosure | 2,536 | 2,396
Fair value, inputs, level 2 | Fair value, measurements, recurring |  |
Fair value measurements [Line Items] |  |
Assets, fair value disclosure | 116,232 | 130,895
Fair value, inputs, level 2 | Fair value, measurements, recurring | Money market funds |  |
Fair value measurements [Line Items] |  |
Assets, fair value disclosure | 7,361 | 10,190
Fair value, inputs, level 2 | Fair value, measurements, recurring | Insurance contracts* |  |
Fair value measurements [Line Items] |  |
Assets, fair value disclosure | 98,041 | 109,603
Fair value, inputs, level 2 | Fair value, measurements, recurring | Mortgage-backed securities |  |
Fair value measurements [Line Items] |  |
Assets, fair value disclosure | 8,294 | 8,706
Fair value, inputs, level 2 | Fair value, measurements, recurring | U.S. Treasury securities |  |
Fair value measurements [Line Items] |  |
Assets, fair value disclosure | $ 2,536 | $ 2,396

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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 -Subparagraph (a) -URI https://asc.fasb.org/extlink&oid=126976982&loc=d3e19207-110258 + Details
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