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Related Party Transactions (Narrative) (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
	Jun. 01, 2023	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Related Party Transaction [Line Items]
Services and other revenues		$ 725,627	$ 691,653	$ 1,963,779	$ 1,962,585
Reinsurance recoverables		8,534,919		8,534,919		$ 8,446,745
ISIC [Member]
Related Party Transaction [Line Items]
Gain on sale of business	$ 16,900
Nephila Reinsurers [Member]
Related Party Transaction [Line Items]
Reinsurance recoverables		874,100		874,100		1,400,000
Hagerty, Inc. [Member]
Related Party Transaction [Line Items]
Reinsurance recoverables		200,000		200,000		$ 159,700
Insurance-linked Securities Operations [Member] | Unconsolidated entities managed by Nephila [Member]
Related Party Transaction [Line Items]
Services and other revenues		$ 43,600	$ 17,100	$ 74,100	$ 57,000

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Amount of gain (loss) from sale and disposal of integrated set of activities and assets capable of being conducted and managed for purpose of providing return in form of dividend, lower cost, or other economic benefit to investor, owner, member and participant.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 230
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 28
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482740/230-10-45-28

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 810
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-Section 50
-Paragraph 1B
-Subparagraph (a)
-Publisher FASB
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Amount, after valuation allowance, recoverable under reinsurance contracts. Examples include, but are not limited to, settled and unsettled claims, incurred but not reported losses, loss adjustment expense, policy benefits and policy reserves. Excludes premiums paid under reinsurance contracts.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 944
-SubTopic 310
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479584/944-310-50-2

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 944
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479838/944-20-50-5

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 944
-SubTopic 310
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Reference 4: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 944
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-Section 45
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-URI https://asc.fasb.org//1943274/2147479616/944-310-45-6

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
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-Section 50
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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.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07(2)(c)(2)(i))
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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