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Reserve for Loss and Loss Expense (Reserve Loss Development) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Favorable or adverse loss development	$ (78,890)	$ (82,853)	$ (72,932)
Favorable or unfavorable loss development [Member]
Favorable or adverse loss development	(78,900)	(82,900)	(72,900)
Favorable or unfavorable loss development [Member] | Commercial Automobile [Member]
Favorable or adverse loss development	22,500	13,300	7,100
Favorable or unfavorable loss development [Member] | General Liability [Member]
Favorable or adverse loss development	(5,000)	(29,000)	(35,000)
Favorable or unfavorable loss development [Member] | Commercial Automobile [Member]
Favorable or adverse loss development	22,500	13,300	7,100
Favorable or unfavorable loss development [Member] | Workers Compensation [Member]
Favorable or adverse loss development	(70,000)	(58,000)	(60,000)
Favorable or unfavorable loss development [Member] | Business Owners' Policies [Member]
Favorable or adverse loss development	(7,300)	(400)	3,900
Favorable or unfavorable loss development [Member] | Commercial Property [Member]
Favorable or adverse loss development	(1,600)	(2,600)	9,200
Favorable or unfavorable loss development [Member] | Bonds [Member]
Favorable or adverse loss development	(10,000)	0	0
Favorable or unfavorable loss development [Member] | Homeowners [Member]
Favorable or adverse loss development	(600)	1,800	7,700
Favorable or unfavorable loss development [Member] | Personal Automobile [Member]
Favorable or adverse loss development	500	(200)	(1,800)
Favorable or unfavorable loss development [Member] | E&S Casualty Lines [Member]
Favorable or adverse loss development	(5,000)	(7,000)	0
Favorable or unfavorable loss development [Member] | E&S Property Lines [Member]
Favorable or adverse loss development	(2,500)	(800)	(4,000)
Favorable or unfavorable loss development [Member] | Insurance, Other [Member]
Favorable or adverse loss development	(100)	0	0
Favorable or unfavorable loss development [Member] | Property Insurance [Member]
Favorable or adverse loss development	7,100	(1,900)	12,100
Favorable or unfavorable loss development [Member] | Casualty Insurance Product Line [Member]
Favorable or adverse loss development	(86,000)	(81,000)	(85,000)
Favorable or unfavorable loss development [Member] | Casualty Insurance Product Line [Member] | Commercial Automobile [Member]
Favorable or adverse loss development	$ 15,000	$ 15,000	$ 10,000

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
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 40
-Section 50
-Paragraph 3
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=116884095&loc=d3e14764-158437

+ Details

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