Borrowings and Financing Activities - Narrative (Details) - USD ($)	1 Months Ended	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2024	Mar. 31, 2023	Apr. 30, 2024	Jan. 31, 2024	Dec. 31, 2023
Debt Instrument [Line Items]
Repayments in cash		$ 527,079,000	$ 0
Loss on extinguishment of debt		4,275,000	$ 0
Collateral	$ 6,327,114,000	6,327,114,000				$ 6,085,654,000
Mortgage loans held for sale | Asset Pledged as Collateral
Debt Instrument [Line Items]
Collateral	142,000,000	142,000,000				31,000,000
Total fixed-maturities available for sale | Fixed maturities AFS and trading securities
Debt Instrument [Line Items]
FHLB, collateral pledged	84,000,000	84,000,000				101,000,000
Senior notes
Debt Instrument [Line Items]
Outstanding borrowings	1,512,860,000	$ 1,512,860,000				1,417,781,000
FHLB advances | Minimum
Debt Instrument [Line Items]
FHLB, ratio of market value of collateral to advances		1.03
FHLB advances | Maximum
Debt Instrument [Line Items]
FHLB, ratio of market value of collateral to advances		1.14
Mortgage loan financing facilities | Goldman Sachs Master Repurchase Agreement
Debt Instrument [Line Items]
Long-term debt	100,000,000	$ 100,000,000
Mortgage loan financing facilities | BMO Master Repurchase Agreement
Debt Instrument [Line Items]
Maximum borrowing capacity	150,000,000	150,000,000
Mortgage loan financing facilities | BMO Master Repurchase Agreement | Subsequent Event
Debt Instrument [Line Items]
Maximum borrowing capacity				$ 400,000,000
Mortgage loan financing facilities | Flagstar Bank Master Repurchase Agreement
Debt Instrument [Line Items]
Maximum borrowing capacity					$ 150,000,000
Revolving Credit Facility
Debt Instrument [Line Items]
Fair value of amount outstanding	0	0
Revolving Credit Facility | Unsecured Revolving Credit Facility, Expiration Date 2026
Debt Instrument [Line Items]
Current borrowing capacity	275,000,000	275,000,000
Senior Notes due 2029 | Senior notes
Debt Instrument [Line Items]
Aggregate principal amount	625,000,000	$ 625,000,000
Net proceeds received	$ 617,000,000
Interest rate on senior notes	6.20%	6.20%
Redemption price, percentage of principal amount		100.00%
Basis spread on variable rate		0.30%
Stock retention percentage required in order to make capital stock transactions	80.00%	80.00%
Outstanding borrowings	$ 616,845,000	$ 616,845,000				0
Senior Notes due 2025 | Senior notes
Debt Instrument [Line Items]
Interest rate on senior notes	6.625%	6.625%
Redemption price, percentage of principal amount	100.40%
Aggregate principal redemption amount	$ 525,000,000
Repayments in cash	527,000,000
Loss on extinguishment of debt	4,000,000
Outstanding borrowings	$ 0	$ 0				$ 522,343,000