Investments - Net Investment Income (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Net Investment Income [Line Items]
Gross investment income, operating		$ 56,183	$ 51,173	$ 111,910	$ 100,899
Investment expenses		(2,072)	(2,167)	(4,208)	(4,395)
Investment income net of investment expenses		54,111	49,006	107,702	96,504
Interest expense on surplus note		(15,659)	(16,608)	(31,444)	(33,042)
Net investment income		38,452	32,398	76,258	63,462
Equity Securities [Member]
Net Investment Income [Line Items]
Gross investment income, operating		323	380	712	760
Policy Loans and Other Invested Assets [Member]
Net Investment Income [Line Items]
Gross investment income, operating		543	352	1,005	281
Cash, Cash Equivalents and Short-Term Investments [Member]
Net Investment Income [Line Items]
Gross investment income, operating		6,640	5,840	13,621	10,968
Total return on deposit asset underlying 10% insurance agreement [Member]
Net Investment Income [Line Items]
Gross investment income, operating	[1]	2,400	1,636	4,574	3,685
Available-for-Sale [Member] | Fixed Maturities
Net Investment Income [Line Items]
Gross investment income, operating		30,618	26,357	60,554	52,163
Held-to-Maturity [Member] | Fixed Maturities
Net Investment Income [Line Items]
Gross investment income, operating		$ 15,659	$ 16,608	$ 31,444	$ 33,042

[1] Includes $0.2 million and $0.1 million of net gains (losses) recognized for the change in fair value of the deposit asset underlying the 10% coinsurance agreement for the three and six months ended June 30, 2024, respectively. Includes $(0.9) million and $(1.2) million of net gains (losses) recognized for the change in fair value of the deposit asset underlying the 10% coinsurance agreement for the three and six months ended June 30, 2023, respectively.