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Related Party Transactions (Narrative) (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
	Jun. 01, 2023	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022	Dec. 31, 2022
Related Party Transaction [Line Items]
Services and other revenues		$ 672,291	$ 639,992	$ 1,238,152	$ 1,270,932
Reinsurance recoverables		8,296,043		8,296,043		$ 8,446,745
Nephila Reinsurers [Member]
Related Party Transaction [Line Items]
Reinsurance recoverables		949,300		949,300		1,400,000
ISIC [Member]
Related Party Transaction [Line Items]
Gain on sale of business	$ 16,900
Hagerty, Inc. [Member]
Related Party Transaction [Line Items]
Reinsurance recoverables		178,200		178,200		$ 159,700
Insurance-linked Securities Operations [Member] | Unconsolidated entities managed by Nephila [Member]
Related Party Transaction [Line Items]
Services and other revenues		$ 20,800	$ 17,500	$ 30,600	$ 39,900

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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
-SubTopic 10
-Name Accounting Standards Codification
-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
-Name Accounting Standards Codification
-Section 45
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Reference 4: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 944
-SubTopic 310
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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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-Publisher FASB
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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))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483575/946-220-S99-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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