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Fair value measurements (Details 3) - USD ($) $ in Thousands | Mar. 31, 2022 | Dec. 31, 2021 | Mar. 31, 2021
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Concentration risks, percentage [Abstract] |  |  |
Percentage in fixed-income and other investments | 61.00% | 61.00% | 54.00%
Percentage investment in common stock of large-cap companies | 17.00% | 17.00% | 19.00%
Percentage investment in common stock of mid-cap companies | 8.00% | 8.00% | 10.00%
Percentage investment in common stock of small-cap companies | 6.00% | 7.00% | 9.00%
Percentage investment in target date investments | 6.00% | 5.00% | 6.00%
Percentage investment in cash and cash equivalents | 2.00% | 2.00% | 2.00%
Fair value, measurements, recurring |  |  |
Fair value measurements [Line Items] |  |  |
Assets, fair value disclosure | $ 129,598 | $ 130,895 | $ 122,496
Fair value, inputs, level 2 | Fair value, measurements, recurring |  |  |
Fair value measurements [Line Items] |  |  |
Assets, fair value disclosure | 129,598 | 130,895 | 122,496
Money market funds | Fair value, measurements, recurring |  |  |
Fair value measurements [Line Items] |  |  |
Assets, fair value disclosure | 13,131 | 10,190 | 9,388
Money market funds | Fair value, inputs, level 2 | Fair value, measurements, recurring |  |  |
Fair value measurements [Line Items] |  |  |
Assets, fair value disclosure | 13,131 | 10,190 | 9,388
Insurance contracts* | Fair value, measurements, recurring |  |  |
Fair value measurements [Line Items] |  |  |
Assets, fair value disclosure | 105,371 | 109,603 | 101,632
Insurance contracts* | Fair value, inputs, level 2 | Fair value, measurements, recurring |  |  |
Fair value measurements [Line Items] |  |  |
Assets, fair value disclosure | 105,371 | 109,603 | 101,632
Mortgage-backed securities | Fair value, measurements, recurring |  |  |
Fair value measurements [Line Items] |  |  |
Assets, fair value disclosure | 8,471 | 8,706 | 8,854
Mortgage-backed securities | Fair value, inputs, level 2 | Fair value, measurements, recurring |  |  |
Fair value measurements [Line Items] |  |  |
Assets, fair value disclosure | 8,471 | 8,706 | 8,854
U.S. Treasury securities | Fair value, measurements, recurring |  |  |
Fair value measurements [Line Items] |  |  |
Assets, fair value disclosure | 2,625 | 2,396 | 2,622
U.S. Treasury securities | Fair value, inputs, level 2 | Fair value, measurements, recurring |  |  |
Fair value measurements [Line Items] |  |  |
Assets, fair value disclosure | $ 2,625 | $ 2,396 | $ 2,622

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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 http://asc.fasb.org/extlink&oid=123874694&loc=d3e19207-110258 + Details
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