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Reserve for Loss and Loss Expense (Reserve Loss Development narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Increase of net loss and loss expense reserves	$ 331,000	$ 385,000	$ 296,200
Anticipated recoveries for salvage and subrogation claims	116,000	91,300	87,000
Prior year development	(9,954)	(78,890)	(82,853)
Favorable or unfavorable loss development [Member]
Prior year development	$ (10,000)	$ (78,900)	$ (82,900)

X

- Definition

Amount of increase (decrease) in liability to reflect the estimated ultimate cost of settling claims relating to insured events that have occurred on or before the balance sheet date, whether or not reported to the insurer at that date.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 45
-Paragraph 28
-Subparagraph (a)
-SubTopic 10
-Topic 230
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482740/230-10-45-28

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

The estimated amount as of the balance sheet date to be received by an insurer from the sale of property (usually damaged) on which the insurer has paid a total claim to the insured and has obtained title to the property and the right of an insurer to pursue any course of recovery of damages, in its name or in the name of the policyholder, against a third party who is liable for costs relating to an insured event that have been paid by the insurer. Estimated salvage and subrogation is generally deducted from the liability for unpaid claims.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 944
-SubTopic 40
-Section 30
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479224/944-40-30-2

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 944
-SubTopic 40
-Section 30
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479224/944-40-30-3

+ Details

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Balance Type:	debit
Period Type:	instant

X

- Definition

Amount, after effects of reinsurance, of expense (reversal of expense) for claims incurred in prior reporting periods and related claims settlement costs.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
-SubTopic 40
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480081/944-40-50-3

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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X

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: