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Segment Reporting Disclosures (Reconciliation Of Segment Assets To The Company's Consolidated Balance Sheets (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Segment Reporting Information [Line Items]
Assets	$ 39,067,626	$ 37,473,815
Other [Member]
Segment Reporting Information [Line Items]
Assets	5,999,200	6,171,708
Segment assets [Member]
Segment Reporting Information [Line Items]
Assets	33,068,426	31,302,107
Segment assets [Member] | Investing [Member]
Segment Reporting Information [Line Items]
Assets	22,097,531	22,129,633
Segment assets [Member] | Underwriting [Member]
Segment Reporting Information [Line Items]
Assets	7,229,312	6,621,639
Segment assets [Member] | Markel Ventures [Member]
Segment Reporting Information [Line Items]
Assets	$ 3,741,583	$ 2,550,835

X

- 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

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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.

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