Investments - Net Investment Income (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Net Investment Income [Line Items]
Gross investment income, operating		$ 209,995	$ 163,330	$ 147,551
Investment expenses		(8,684)	(6,343)	(4,756)
Investment income net of investment expenses		201,311	156,987	142,795
Interest expense on surplus note		(65,474)	(63,922)	(62,207)
Net investment income		135,837	93,065	80,588
Equity Securities [Member]
Net Investment Income [Line Items]
Gross investment income, operating		1,523	1,509	1,632
Policy Loans and Other Invested Assets [Member]
Net Investment Income [Line Items]
Gross investment income, operating		1,297	1,046	1,019
Cash, Cash Equivalents and Short-Term Investments [Member]
Net Investment Income [Line Items]
Gross investment income, operating		23,601	5,943	456
Total return on deposit asset underlying 10% insurance agreement [Member]
Net Investment Income [Line Items]
Gross investment income, operating	[1]	9,338	(65)	1,875
Available-for-Sale [Member] | Fixed Maturities
Net Investment Income [Line Items]
Gross investment income, operating		108,762	90,975	80,362
Held-to-Maturity [Member] | Fixed Maturities
Net Investment Income [Line Items]
Gross investment income, operating		$ 65,474	$ 63,922	$ 62,207

[1] Includes $(0.4) million, $(3.8) million, and $(2.5) of net gains (losses) recognized for the change in fair value of the deposit asset underlying the 10% coinsurance agreement for the years ended December 31, 2023, 2022, and 2021, respectively.