Investment income and net realized and unrealized gains - Income from Investments and Net Realized and Unrealized Gains (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Investment income	$ 22,421	$ 16,855	$ 18,607
Net realized and unrealized gains (losses):
Realized gains	6,212	13,015	2,231
Realized losses	(5,142)	(6,414)	(1,598)
Net unrealized investment gains (losses) recognized on equity securities still held	(2,546)	17,720	(2,311)
Investment and other gains (losses) – net	(1,476)	24,321	(1,678)
Debt securities
Debt Securities, Available-for-sale [Line Items]
Investment income	14,483	13,313	15,026
Equity securities, short-term investments, cash equivalents and other
Debt Securities, Available-for-sale [Line Items]
Investment income	$ 7,938	$ 3,542	$ 3,581

Investment And Other Gains (Losses), Net [Abstract]

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Investments, Realized Gain

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Investments, Realized Loss

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Amount of unrealized gain (loss) on investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(3)(d))
-URI https://asc.fasb.org/extlink&oid=120400993&loc=SL114874131-224263

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 321
-SubTopic 10
-Section 50
-Paragraph 4
-URI https://asc.fasb.org/extlink&oid=126980263&loc=SL75117546-209714

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Amount, after investment expense, of income earned from investments in securities and real estate. Includes, but is not limited to, real estate investment, policy loans, dividends, and interest. Excludes realized gain (loss) on investments.

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Amount of gain (loss) related to nonoperating activities, classified as other.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.7,9)
-URI https://asc.fasb.org/extlink&oid=126953954&loc=SL114868664-224227

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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.

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