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Reserve for Loss and Loss Expense (Reserve Loss Development Table Summary) (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Prior year development | $ (9,954) | $ (78,890) | $ (82,853)
Favorable or unfavorable loss development [Member] |  |  |
Prior year development | (10,000) | (78,900) | (82,900)
Favorable or unfavorable loss development [Member] | General Liability [Member] |  |  |
Prior year development | (55,000) | (5,000) | (29,000)
Favorable or unfavorable loss development [Member] | Commercial Automobile [Member] |  |  |
Prior year development | (8,000) | (22,500) | (13,300)
Favorable or unfavorable loss development [Member] | Workers Compensation [Member] |  |  |
Prior year development | (74,500) | (70,000) | (58,000)
Favorable or unfavorable loss development [Member] | Business Owners' Policies [Member] |  |  |
Prior year development | (7,600) | (7,300) | (400)
Favorable or unfavorable loss development [Member] | Commercial Property [Member] |  |  |
Prior year development | (700) | (1,600) | (2,600)
Favorable or unfavorable loss development [Member] | Bonds [Member] |  |  |
Prior year development | 0 | (10,000) | 0
Favorable or unfavorable loss development [Member] | Homeowners [Member] |  |  |
Prior year development | (4,600) | (600) | (1,800)
Favorable or unfavorable loss development [Member] | Personal Automobile [Member] |  |  |
Prior year development | (15,300) | (500) | (200)
Favorable or unfavorable loss development [Member] | E&S Casualty Lines [Member] |  |  |
Prior year development | (5,000) | (5,000) | (7,000)
Favorable or unfavorable loss development [Member] | E&S Property Lines [Member] |  |  |
Prior year development | (1,600) | (2,500) | (800)
Favorable or unfavorable loss development [Member] | Insurance, Other [Member] |  |  |
Prior year development | (100) | (100) | 0
Favorable or unfavorable loss development [Member] | Property Insurance [Member] |  |  |
Prior year development | (16,500) | (7,100) | (1,900)
Favorable or unfavorable loss development [Member] | Casualty Insurance Product Line [Member] |  |  |
Prior year development | $ (6,500) | $ (86,000) | $ (81,000)

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- Definition Amount, after effects of reinsurance, of expense (reversal of expense) for claims incurred in prior reporting periods and related claims settlement costs. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 40 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480081/944-40-50-3 + Details
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