Liability for Future Policyholder Benefits - Reconciliation of the Net Liability for Future Benefits to Life and Health Insurance Reserves (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Jun. 30, 2023	Dec. 31, 2022	Jun. 30, 2022	Dec. 31, 2021
Insurance [Abstract]
Present Value of Expected Future Policyholder benefits	$ 3,330,500	$ 3,441,900	$ 3,330,500	$ 3,441,900
Net Liability for Future Policyholder Benefits	2,644,100	2,820,100	2,644,100	2,820,100
Deferred Profit Liability	304,900	249,900	304,900	249,900
A&H and Other Reserves	149,100	149,800	149,100	149,800
Total Life and Health Insurance Reserves	3,098,100	3,219,800	3,098,100	3,219,800
Liability for Future Policy Benefit, by Product Segment [Line Items]
Net Liability for Future Policyholder Benefits	2,644,100	2,820,100	2,644,100	2,820,100
Deferred Profit Liability	304,900	249,900	304,900	249,900
A&H and Other Reserves	149,100	149,800	149,100	149,800
Total Life and Health Insurance Reserves	3,098,100	3,219,800	3,098,100	3,219,800
Term Life Insurance
Insurance [Abstract]
Gross Premiums or Assessments	98,400	100,800	300,700	297,200
Interest Expense	35,400	35,400	106,100	106,500
Liability for Future Policy Benefit, by Product Segment [Line Items]
Net Liability for Future Policyholder Benefits	10,181,500	9,585,400	10,181,500	9,585,400
Liability for Future Policy Benefit, Expected Future Gross Premium, Undiscounted, before Reinsurance	4,446,400	3,801,100	4,446,400	3,801,100
Liability for Future Policy Benefit, Expected Future Gross Premium, Discounted, before Reinsurance	2,748,000	2,585,100	2,748,000	2,585,100
Gross Premiums or Assessments	98,400	100,800	300,700	297,200
Interest Expense	$ 35,400	$ 35,400	$ 106,100	$ 106,500
Liability for Future Policy Benefit, Weighted-Average Interest Accretion Rate	4.57%	4.59%	4.57%	4.59%
Liability for Future Policy Benefit, Current Weighted-Average Discount Rate	5.88%	5.44%	5.88%	5.44%
Term Life Insurance | Effect of Retrospective Application of Accounting Standards Update 2018-12
Insurance [Abstract]
Present Value of Expected Future Policyholder benefits					$ 3,635,900	$ 3,561,000	$ 3,799,400	$ 4,933,100
Liability for Future Policy Benefit, by Product Segment [Line Items]
Net Liability for Future Policyholder Benefits	$ 2,644,100	$ 2,820,100	$ 2,644,100	$ 2,820,100