The amount of retirees and beneficiaries impacted by the purchase of an irrevocable group annuity contract.

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Target allocation maximum percentage of investment in a single equity security to total plan assets without prior approval of plan administrator.

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The number of investment companies actively managing plan assets.

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Number Of Investments The Companys Pension Plan Held Which Individually Exceed 10 Percent Of Total Plan Assets

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The percentage of plan assets managed by investment companies.

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The percentage of plan assets managed internally by the Company.

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For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

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Amount of cost of providing special or contractual termination benefits payable from defined benefit plan.

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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.

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No definition available.

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Percentage of target investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan.

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Amount of gain (loss) recognized in net periodic benefit (cost) credit from irrevocable action relieving primary responsibility for benefit obligation and eliminating risk related to obligation and assets used to effect settlement.

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Amount of (increase) decrease to benefit obligation of defined benefit plan from irrevocable action relieving primary responsibility for benefit obligation and eliminating risk for obligation and assets used to effect settlement. Includes, but is not limited to, lump-sum cash payment to participant in exchange for right to receive specified benefits, purchase of nonparticipating annuity contract and change from remeasurement.

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Amount of payment, which decreases plan assets of defined benefit plan, for irrevocable action relieving primary responsibility for benefit obligation and eliminating risk for obligation and assets used to effect settlement. Transaction constituting settlement includes, but is not limited to, making lump-sum cash payment to participant in exchange for their rights to receive specified benefits and purchasing nonparticipating annuity contract.

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Percentage of actual investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan.

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Sum of the carrying amounts as of the balance sheet date of all investments.

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Pension and Postretirement Plans (Narrative) (Details) - Defined Benefit Pension Plan [Member] $ in Thousands	1 Months Ended	3 Months Ended							9 Months Ended
	Oct. 31, 2024 USD ($) retirees_beneficiaries	Dec. 31, 2024 USD ($)	Sep. 30, 2024 USD ($) investment company	Jun. 30, 2024 USD ($)	Mar. 31, 2024 USD ($)	Sep. 30, 2023 USD ($)	Jun. 30, 2023 USD ($)	Mar. 31, 2023 USD ($)	Sep. 30, 2024 USD ($) investment company	Sep. 30, 2023 USD ($)	Dec. 31, 2023 USD ($) investment
Defined Benefit Plan Disclosure [Line Items]
Early retirement programs and special separation benefit expense			$ 3,665			$ 0			$ 20,493	$ 9,646
Percent of plan assets managed internally by the company									48.00%
Percent of plan assets managed by investment companies									52.00%
Number of investment companies actively managing plan assets \| company			2						2
Percentage of total plan assets			100.00%						100.00%		100.00%
Markel Corporation [Member]
Defined Benefit Plan Disclosure [Line Items]
Value of investments			$ 91,000						$ 91,000		$ 82,400
Berkshire Hathaway Common Stock [Member] \| Investment Manager 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, target allocation maximum percentage of assets, singular equity security, without prior approval by plan administrator									20.00%
Alphabet and Berkshire Hathaway Common Stock [Member] \| Investment Manager 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, target allocation maximum percentage of assets, singular equity security, without prior approval by plan administrator									15.00%
Foreign Investments [Member] \| Maximum [Member] \| Investment Manager 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, target allocation percentage of assets			35.00%						35.00%
Foreign Investments [Member] \| Maximum [Member] \| Investment Manager 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, target allocation percentage of assets			15.00%						15.00%
Private investment fund [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of total plan assets			16.00%						16.00%		17.00%
Single Equity Concentration [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, target allocation maximum percentage of assets, singular equity security, without prior approval by plan administrator									10.00%
Value of investments			$ 1,736,100						$ 1,736,100		$ 1,011,100
Percentage of total plan assets			51.00%						51.00%		34.00%
Single Equity Concentration [Member] \| Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Number of investments the company's pension plan held which individually exceed 10% of total plan assets \| investment			1						1		1
Single Equity Concentration [Member] \| Private investment fund [Member]
Defined Benefit Plan Disclosure [Line Items]
Number of investments the company's pension plan held which individually exceed 10% of total plan assets \| investment			1						1		1
Single Equity Concentration [Member] \| US Treasury Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Number of investments the company's pension plan held which individually exceed 10% of total plan assets \| investment			1						1
Concentration In Single Entity, Type Of Industry, Foreign Country Or Individual Fund [Member] \| Defined Benefit Plan Assets Total [Member]
Defined Benefit Plan Disclosure [Line Items]
Minimum percentage of plan assets considered as significant concentrations in pension plans									10.00%
Leaf Group and Code3 [Member] \| Separation Incentive Program [Member]
Defined Benefit Plan Disclosure [Line Items]
Early retirement programs and special separation benefit expense								$ 4,100
Kaplan, Graham Media Group, Leaf Group, Code3 and Pinna [Member] \| Separation Incentive Program [Member]
Defined Benefit Plan Disclosure [Line Items]
Early retirement programs and special separation benefit expense							$ 5,500
Framebridge [Member] \| Separation Incentive Program [Member]
Defined Benefit Plan Disclosure [Line Items]
Early retirement programs and special separation benefit expense					$ 400
Graham Media Group and Corporate [Member] \| VoluntaryRetirementIncentiveProgram [Member]
Defined Benefit Plan Disclosure [Line Items]
Early retirement programs and special separation benefit expense				$ 14,800
Framebridge and Code3 [Member] \| Separation Incentive Program [Member]
Defined Benefit Plan Disclosure [Line Items]
Early retirement programs and special separation benefit expense				$ 1,600
Kaplan, Dekko, WGB, Saatchi Art, Society6, Slate and Decile [Member] \| Separation Incentive Program [Member]
Defined Benefit Plan Disclosure [Line Items]
Early retirement programs and special separation benefit expense			$ 3,700
Subsequent Event [Member] \| Irrevocable Group Annuity Contract Purchase [Member]
Defined Benefit Plan Disclosure [Line Items]
Payment for settlement	$ 461,300
Settlement of obligation	$ 457,900
Number of retirees and beneficiaries \| retirees_beneficiaries	1,850
Subsequent Event [Member] \| Forecast [Member] \| Irrevocable Group Annuity Contract Purchase [Member]
Defined Benefit Plan Disclosure [Line Items]
Settlement gain		$ 700,000