Reserves For Losses And Loss Expenses (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Reserves For Losses And Loss Expenses [Line Items]
Liability recognized for best estimate net of reinsurance	$ 381,000
Liability recognized for best estimate net of reinsurance, incurred but not reported (IBNR)	2,000
Favorable reserve development net of premium offsets	4,432	$ (18,899)	$ (36,405)
Reserve for losses and loss adjustment expenses relating to asbestos and environmental claims, net	16,000	17,000
Workers' Compensation Discount, Prior Year Amount	1,358,000	1,352,000
Workers' compensation discount after effects of ceded reinsurance, amount	405,000	390,000
Liability recognized for best estimate net of reinsurance, reported losses	$ 379,000
Minimum
Reserves For Losses And Loss Expenses [Line Items]
Workers' compensation discount, percent	0.70%
Maximum
Reserves For Losses And Loss Expenses [Line Items]
Workers' compensation discount, percent	6.50%
Weighted Average
Reserves For Losses And Loss Expenses [Line Items]
Workers' compensation discount, percent	3.60%
Discounted [Member]
Reserves For Losses And Loss Expenses [Line Items]
Workers' compensation discount, percent	3.00%
Insurance
Reserves For Losses And Loss Expenses [Line Items]
Liability recognized for best estimate net of reinsurance	$ 326,000
Unfavorable reserve development net of premium offsets	8,000	21,000	41,000
Reinsurance & Monoline Excess
Reserves For Losses And Loss Expenses [Line Items]
Liability recognized for best estimate net of reinsurance	55,000
Favorable reserve development net of premium offsets	$ 12,000	$ 2,000	$ 5,000
Excess workers' compensation
Reserves For Losses And Loss Expenses [Line Items]
Workers' compensation discount, percent	97.00%