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Pension Plans (Narrative) (Details) - Defined Benefit Pension Plan [Member] $ in Thousands	1 Months Ended	3 Months Ended				6 Months Ended		9 Months Ended
	Jun. 30, 2026 USD ($) investment company numberOfRetireesAndBeneficiaries	Jun. 30, 2026 USD ($) investment company	Mar. 31, 2026 USD ($)	Jun. 30, 2025 USD ($)	Mar. 31, 2025 USD ($)	Jun. 30, 2026 USD ($) investment company	Jun. 30, 2025 USD ($)	Sep. 30, 2025	Dec. 31, 2025 USD ($) investment
Defined Benefit Plan Disclosure [Line Items]
Settlement gain		$ 136,955		$ 0		$ 136,955	$ 0
Early retirement and separation program costs		$ 3,837		6,015		$ 7,937	$ 6,639
Percent of plan assets managed internally by the company						41.00%
Percent of plan assets managed by investment companies						59.00%
Number of investment companies actively managing plan assets \| company	2	2				2
Percentage of total plan assets	100.00%	100.00%				100.00%			100.00%
Irrevocable Group Annuity Contract Purchase [Member]
Defined Benefit Plan Disclosure [Line Items]
Payment for settlement	$ 113,900
Settlement of obligation	$ 124,300
Number of retirees and beneficiaries \| numberOfRetireesAndBeneficiaries	1,080
Settlement gain	$ 137,000
Markel Corporation [Member]
Defined Benefit Plan Disclosure [Line Items]
Value of investments	$ 113,300	$ 113,300				$ 113,300			$ 124,700
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	50.00%	50.00%				50.00%
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%				15.00%
Private investment fund [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of total plan assets	17.00%	17.00%				17.00%			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	$ 1,232,000	$ 1,232,000				$ 1,232,000			$ 1,267,400
Percentage of total plan assets	37.00%	37.00%				37.00%			37.00%
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			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			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%		10.00%
Dekko [Member] \| Voluntary Retirement Incentive Program [Member]
Defined Benefit Plan Disclosure [Line Items]
Early retirement and separation program costs		$ 2,000
Kaplan, Graham Media Group, Code3 and Slate [Member] \| Separation Incentive Program [Member]
Defined Benefit Plan Disclosure [Line Items]
Early retirement and separation program costs		$ 1,900
Kaplan, Graham Media Group, Joyce, Dekko, Framebridge, Code3, Slate and Corporate [Member] \| Separation Incentive Program [Member]
Defined Benefit Plan Disclosure [Line Items]
Early retirement and separation program costs			$ 4,100
Kaplan, Graham Media Group, WGB, Saatchi Art, Society6, Code3 and Decile [Member] \| Separation Incentive Program [Member]
Defined Benefit Plan Disclosure [Line Items]
Early retirement and separation program costs				$ 6,000
World of Good Brands [Member] \| Separation Incentive Program [Member]
Defined Benefit Plan Disclosure [Line Items]
Early retirement and separation program costs					$ 600