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Reserve for Loss and Loss Expense (Reserve Loss Development Table Summary) (Details) - USD ($) $ in Thousands	12 Months Ended
	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)

X

- 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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