Reserves for Loss and Loss Expenses (Narrative) (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022
Liability for Claims and Claims Adjustment Expense [Line Items]
Net of loss reserves discount	$ 22,000	$ 15,000
Increase (decrease) in estimates for claims	6,000	(22,000)
Adjustment expense	21,000	3,000
Liability recognized for best estimate net of reinsurance	352,000
Liability recognized for best estimate net of reinsurance, current accident year losses	259
Liability recognized for best estimate net of reinsurance, reported losses	348,000
Liability recognized for best estimate net of reinsurance, incurred but not reported (IBNR)	4,000
Insurance
Liability for Claims and Claims Adjustment Expense [Line Items]
Liability recognized for best estimate net of reinsurance	298,000
Unfavorable reserve development net of premium offsets	25,000
Favorable reserve development net of premium offsets		3,000
Reinsurance & Monoline Excess
Liability for Claims and Claims Adjustment Expense [Line Items]
Liability recognized for best estimate net of reinsurance	54,000
Unfavorable reserve development net of premium offsets		$ 300
Favorable reserve development net of premium offsets	$ 4,000