The Company's investment in one of the unconsolidated Funds.

No definition available.

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- Definition

Net investment and insurance assets under management related to unconsolidated variable interest entities.

+ References

No definition available.

+ Details

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- Definition

Sum of the carrying amounts as of the balance sheet date of all assets that are recognized. Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(11))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 22
-URI http://asc.fasb.org/extlink&oid=115929826&loc=d3e8736-108599

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(12))
-URI http://asc.fasb.org/extlink&oid=119400593&loc=d3e572229-122910

+ Details

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- Definition

Amount of purchases of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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- Definition

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.

+ Details

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- Details

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- Details

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- Details

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- Details

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Variable Interest Entities (Narrative) (Details) - USD ($) $ in Thousands		3 Months Ended			6 Months Ended
	Jan. 01, 2020	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Variable Interest Entity [Line Items]
Investment in one of the unconsolidated funds, variable interest entity	$ 90,000	$ 0	$ 90,000	$ 500	$ 90,000	$ 500
Assets		39,067,626			39,067,626		$ 37,473,815
Markel Diversified Fund [Member] \| Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Assets		13,500			13,500		19,600
Unconsolidated Markel CATCo Fund 2 [Member]
Variable Interest Entity [Line Items]
Variable interest entity, consolidated, carrying amount, investment in one of the unconsolidated funds		102,500			102,500		26,800
Unconsolidated Markel CATCo Funds [Member]
Variable Interest Entity [Line Items]
Net assets under management of MCIM for unconsolidated VIEs		$ 2,000,000			$ 2,000,000		$ 2,700,000