Comprehensive Income (Loss) - Schedule of Reclassification out of AOCI (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Net realized and unrealized investment gains (losses)	$ 1,297	$ (5,426)	$ (338)	$ (2,082)
Total federal income tax expense (benefit)	16,779	(15,549)	(3,269)	(37,734)
Loss and loss expense incurred	925,548	646,130	1,629,840	1,213,568
Other insurance expenses	107,773	108,857	223,760	217,445
Income (loss), before federal income tax	(80,098)	74,157	22,468	188,916
Net income (loss)	(63,319)	58,608	19,199	151,182
Reclassification out of AOCI
Net income (loss)	1,772	7,328	4,568	5,221
Reclassification out of AOCI | Defined benefit pension plan
Total federal income tax expense (benefit)	(203)	(159)	(406)	(318)
Loss and loss expense incurred	223	173	445	348
Other insurance expenses	744	584	1,489	1,166
Income (loss), before federal income tax	967	757	1,934	1,514
Net income (loss)	764	598	1,528	1,196
Reclassification out of AOCI | Net realized (gains) losses on disposals and intent-to-sell AFS securities
Net realized and unrealized investment gains (losses)	43	9,383	(35)	15,487
Total federal income tax expense (benefit)	(10)	(1,970)	7	(3,252)
Net income (loss)	33	7,413	(28)	12,235
Reclassification out of AOCI | Credit loss related
Net realized and unrealized investment gains (losses)	1,233	(864)	3,883	(10,393)
Total federal income tax expense (benefit)	(258)	181	(815)	2,183
Net income (loss)	$ 975	$ (683)	$ 3,068	$ (8,210)