Shareholders' Equity (Roll Forward of AOCI) (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 1,119,714	$ 1,169,889	$ 1,104,018	$ 1,428,387
OCI, before reclassifications, net of tax	(29,492)	(90,233)	(1,248)	(341,563)
Amounts reclassified from AOCI, net of tax	133	180	3,016	1,038
Net OCI, current period	(29,359)	(90,053)	1,768	(340,525)
Ending balance	1,011,843	1,065,996	1,011,843	1,065,996
Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(267,480)	(234,188)	(298,607)	16,284
Ending balance	(296,839)	(324,241)	(296,839)	(324,241)
Unrealized Investment Gains (Losses) on Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(270,325)	(235,045)	(297,142)	14,929
OCI, before reclassifications, net of tax	(33,371)	(90,233)	(9,437)	(341,232)
Amounts reclassified from AOCI, net of tax	133	194	3,016	1,219
Net OCI, current period	(33,238)	(90,039)	(6,421)	(340,013)
Ending balance	(303,563)	(325,084)	(303,563)	(325,084)
Unrealized Investment Gains (Losses) on Cash Flow Hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	4,310		0
OCI, before reclassifications, net of tax	3,879		8,189
Amounts reclassified from AOCI, net of tax	0		0
Net OCI, current period	3,879		8,189
Ending balance	8,189		8,189
Non-credit Impairments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(11)	(331)	(11)	0
OCI, before reclassifications, net of tax	0	0	0	(331)
Amounts reclassified from AOCI, net of tax	0	0	0	0
Net OCI, current period	0	0	0	(331)
Ending balance	(11)	(331)	(11)	(331)
Unrecognized Change in Defined Benefit Plan Liabilities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(1,454)	1,188	(1,454)	1,355
OCI, before reclassifications, net of tax	0	0	0	0
Amounts reclassified from AOCI, net of tax	0	(14)	0	(181)
Net OCI, current period	0	(14)	0	(181)
Ending balance	$ (1,454)	$ 1,174	$ (1,454)	$ 1,174

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, before reclassification adjustments, of other comprehensive income (loss), attributable to parent.

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Amount after tax of other comprehensive income (loss) attributable to parent entity.

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Amount of equity (deficit) attributable to parent. Excludes temporary equity and equity attributable to noncontrolling interest.

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