Comprehensive Income - Components of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2024	Mar. 31, 2023
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance, December 31, 2023	$ (373,001)
Net current period OCI	(11,971)	$ 67,693
Ending Balance, March 31, 2024	(384,972)
Available-for-Sale Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance, December 31, 2023	(194,628)
OCI before reclassifications	(12,293)
Amounts reclassified from AOCI	(61)
Net current period OCI	(12,354)
Ending Balance, March 31, 2024	(206,982)
Investments Subtotal
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance, December 31, 2023	(279,070)
OCI before reclassifications	(14,767)
Amounts reclassified from AOCI	2,032
Net current period OCI	(12,735)
Ending Balance, March 31, 2024	(291,805)
Credit Loss Related
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance, December 31, 2023	(84,442)
OCI before reclassifications	(2,474)
Amounts reclassified from AOCI	2,093
Net current period OCI	(381)
Ending Balance, March 31, 2024	(84,823)
Defined benefit pension and post-retirement life plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance, December 31, 2023	(93,931)
OCI before reclassifications	0
Amounts reclassified from AOCI	764
Net current period OCI	764
Ending Balance, March 31, 2024	(93,167)
Total AOCI
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance, December 31, 2023	(373,001)
OCI before reclassifications	(14,767)
Amounts reclassified from AOCI	2,796
Net current period OCI	(11,971)	$ 67,693
Ending Balance, March 31, 2024	$ (384,972)

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount, after tax, of accumulated increase (decrease) in equity from transaction and other event and circumstance from nonowner source.

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