XML 60 R47.htm IDEA: XBRL DOCUMENT
v3.20.2

Products, Services and Other Revenues (Schedule Of Receivables And Customer Deposits Related To Contracts With Customers) (Details) - USD ($) $ in Thousands | 6 Months Ended |
--- | --- | ---
Jun. 30, 2020 | Dec. 31, 2019
Receivables and Customer Deposits [Line Items] |  |
Receivables | $ 2,362,789 | $ 1,847,802
Contracts with customers [Member] |  |
Receivables and Customer Deposits [Line Items] |  |
Receivables | 537,126 | 263,904
Customer deposits | 60,255 | $ 60,623
Change in premiums and other receivables, net | $ 273,200 |

X
- Definition Change in Premiums and Other Receivables, Net + References No definition available. + Details
Name: | mkl_ChangeInPremiumsAndOtherReceivablesNet
Namespace Prefix: | mkl_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition [Line Items] for Other Revenue [Table] + References No definition available. + Details
Name: | mkl_OtherRevenueLineItems
Namespace Prefix: | mkl_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of obligation to transfer good or service to customer for which consideration has been received or is receivable. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 606 -SubTopic 10 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=118944033&loc=SL49130531-203044 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 606 -SubTopic 10 -Section 50 -Paragraph 8 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=118956577&loc=SL49130549-203045 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 606 -SubTopic 10 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=118944033&loc=SL49130532-203044 + Details
Name: | us-gaap_ContractWithCustomerLiability
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Carrying amount as of the balance sheet date, net of allowance for doubtful accounts, of all premiums and other types of receivables due from other persons or entities. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.5) -URI http://asc.fasb.org/extlink&oid=119400593&loc=d3e572229-122910 + Details
Name: | us-gaap_PremiumsAndOtherReceivablesNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Details
Name: | us-gaap_ConcentrationRiskByBenchmarkAxis=mkl_CustomerswithContractsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |