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

No definition available.

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- Definition

Percentage of the outstanding preference shares of the investment in one of the unconsolidated Funds.

+ References

No definition available.

+ Details

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- Definition

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

+ References

No definition available.

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- Definition

Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 45
-Paragraph 1A
-URI http://asc.fasb.org/extlink&oid=99377092&loc=SL75136599-209740

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- Definition

Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118956577&loc=SL49130543-203045

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=118956577&loc=SL49130545-203045

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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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Variable Interest Entities (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Variable Interest Entity [Line Items]
Investment management fees earned by the Company from unconsolidated Funds	$ 702,171	$ 628,193	$ 1,244,309	$ 1,067,625
Equity securities	$ 6,875,933		$ 6,875,933		$ 5,720,945
Unconsolidated Markel CATCo Fund 1 [Member]
Variable Interest Entity [Line Items]
Percentage of total assets of the Markel Diversified Fund invested in one of the unconsolidated Funds	2.00%		2.00%		2.00%
Unconsolidated Markel CATCo Fund 2 [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Investment in one of the unconsolidated Funds	$ 26,700		$ 26,700		$ 26,200
CATCo Reinsurance Opportunities Fund Ltd. (CROF) [Member]
Variable Interest Entity [Line Items]
Equity securities	2,400		2,400		$ 4,500
Revenue From Contracts With Customers [Member]
Variable Interest Entity [Line Items]
Investment management fees earned by the Company from unconsolidated Funds	645,094	581,432	1,131,872	978,560
Other [Member]
Variable Interest Entity [Line Items]
Investment management fees earned by the Company from unconsolidated Funds	85,184	49,437	172,559	96,812
Other [Member] \| Revenue From Contracts With Customers [Member]
Variable Interest Entity [Line Items]
Investment management fees earned by the Company from unconsolidated Funds	56,977	26,390	117,614	52,603
Investment Management [Member] \| Revenue From Contracts With Customers [Member]
Variable Interest Entity [Line Items]
Investment management fees earned by the Company from unconsolidated Funds	30,096	17,418	70,988	34,707
Investment Management [Member] \| Other [Member] \| Revenue From Contracts With Customers [Member]
Variable Interest Entity [Line Items]
Investment management fees earned by the Company from unconsolidated Funds	30,096	17,418	70,988	34,707
Unconsolidated Markel CATCo Funds [Member]
Variable Interest Entity [Line Items]
Investment management fees earned by the Company from unconsolidated Funds	8,500	$ 17,400	18,100	$ 34,700
Net Assets of Unconsolidated Variable Interest Entities Under Management	$ 3,100,000		$ 3,100,000