Transactions With Related Parties (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020	Dec. 31, 2019
Related Party Transaction [Line Items]
Purchases of other investments	$ 430,961	$ 228,471
Reinsurance recoverable on unpaid and paid losses and LAE	4,041,076		$ 4,500,802	$ 4,346,816
Premia Holdings Ltd. \| Barbican Group Holdings Limited
Related Party Transaction [Line Items]
Reinsurance recoverable on unpaid and paid losses and LAE	0		199,800
Funds held liability	275,000		$ 149,600
Legacy business, amount of liabilities transferred	$ 380,000

Transfer Of Legacy Business On Acquisition

No definition available.

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- Definition

Amount of funds held as security for payments to be received under reinsurance contracts.

+ References

No definition available.

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- Definition

Amount of cash outflow to acquire investments classified as other.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 13
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3213-108585

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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/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 310
-Section 45
-Paragraph 6
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-Name Accounting Standards Codification
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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

No definition available.

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