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Reserves For Losses And Loss Expenses (Narrative) (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2022 | Dec. 31, 2021 | Dec. 31, 2020
Reserves For Losses And Loss Expenses [Line Items] |  |  |
Liability recognized for best estimate net of reinsurance | $ 341,000 |  |
Liability recognized for best estimate net of reinsurance, incurred but not reported (IBNR) | 4,000 |  |
Favorable reserve development net of premium offsets | (36,405) | $ 6,647 | $ 16,180
Reserve for losses and loss adjustment expenses relating to asbestos and environmental claims, net | 20,000 |  |
Workers' compensation discount, amount | 35,000 | 21,000 | 10,000
Workers' Compensation Discount, Prior Year Amount |  | 1,387,000 |
Workers' compensation discount after effects of ceded reinsurance, amount | 416,000 | 452,000 |
Liability recognized for best estimate net of reinsurance, reported losses | 337,000 |  |
Liability recognized for best estimate net of reinsurance, current accident year losses | $ 5,000 |  |
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 | 3.40% |  |
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 | $ 290,000 |  |
Favorable reserve development net of premium offsets |  | 20,000 | 24,000
Unfavorable reserve development net of premium offsets | (40,000) |  |
Liability recognized for best estimate net of reinsurance, current accident year losses | 3,000 |  |
Reinsurance & Monoline Excess |  |  |
Reserves For Losses And Loss Expenses [Line Items] |  |  |
Liability recognized for best estimate net of reinsurance | 51,000 |  |
Favorable reserve development net of premium offsets | 4,000 |  |
Unfavorable reserve development net of premium offsets |  | $ 13,000 | $ 8,000
Liability recognized for best estimate net of reinsurance, current accident year losses | 2,000 |  |
Short-tail lines |  |  |
Reserves For Losses And Loss Expenses [Line Items] |  |  |
Workers' compensation discount, amount | $ 1,267,000 |  |
Excess workers' compensation |  |  |
Reserves For Losses And Loss Expenses [Line Items] |  |  |
Workers' compensation discount, percent | 97.00% |  |

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- Definition Carrying amount as of the balance sheet date of reserves for the costs of settling insured claims and costs incurred in the claims settlement process attributable to asbestos and environmental claims, net of estimated reinsurance recoveries. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=116884095&loc=d3e14764-158437 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (cc) -URI http://asc.fasb.org/extlink&oid=116884095&loc=d3e14764-158437 + Details
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- Definition Percent discount applied to worker's compensation reserve liability to reduce the reserve to present value. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=116884095&loc=d3e14754-158437 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=124506351&loc=d3e14931-158439 + Details
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- Definition Liability for Claims and Claims Adjustment Expense, Net Of Reinsurance, Current Accident Year Losses + References No definition available. + Details
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- Definition Liability for Claims and Claims Adjustment Expense, Net Of Reinsurance, Reported Claims, Amount + References No definition available. + Details
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