Pension Plans (Narrative) (Details) - Defined Benefit Pension Plan [Member] $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2026 USD ($) company investment	Mar. 31, 2025 USD ($)	Jun. 30, 2025	Dec. 31, 2025 USD ($) investment
Defined Benefit Plan Disclosure [Line Items]
Special separation benefit expense	$ 4,100	$ 624
Percent of plan assets managed internally by the company	43.00%
Percent of plan assets managed by investment companies	57.00%
Number of investment companies actively managing plan assets | company	2
Percentage of total plan assets	100.00%			100.00%
Markel Corporation [Member]
Defined Benefit Plan Disclosure [Line Items]
Value of investments	$ 111,000			$ 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%
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%
Private investment fund [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of total plan assets	18.00%			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	$ 1,199,500			$ 1,267,400
Percentage of total plan assets	38.00%			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
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
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%
Kaplan, Graham Media Group, Joyce, Dekko, Framebridge, Code3, Slate and Corporate [Member] | Separation Incentive Program [Member]
Defined Benefit Plan Disclosure [Line Items]
Special separation benefit expense	$ 4,100
World of Good Brands [Member] | Separation Incentive Program [Member]
Defined Benefit Plan Disclosure [Line Items]
Special separation benefit expense		$ 600