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Investments - Schedule of Pre-Tax Net Investment Income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Net Investment Income [Line Items]
Net investment income earned	$ 138,655	$ 117,759	$ 387,314	$ 334,250
Fixed income securities
Net Investment Income [Line Items]
Net investment income earned	117,242	98,464	338,057	286,501
CMLs
Net Investment Income [Line Items]
Net investment income earned	3,999	3,238	11,375	9,177
Equity securities
Net Investment Income [Line Items]
Net investment income earned	5,164	5,362	13,639	12,147
Short-term investments
Net Investment Income [Line Items]
Net investment income earned	5,712	6,457	17,212	14,656
Alternative investments
Net Investment Income [Line Items]
Net investment income earned	11,769	9,031	22,852	26,429
Other investments
Net Investment Income [Line Items]
Net investment income earned	171	251	565	632
Investment expenses
Net Investment Income [Line Items]
Investment expenses	$ (5,402)	$ (5,044)	$ (16,386)	$ (15,292)

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