Investments - Net Investment Income (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Schedule of Net Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income, operating		$ 163,330	$ 147,551	$ 148,728
Investment expenses		(6,343)	(4,756)	(7,441)
Investment income net of investment expenses		156,987	142,795	141,287
Interest expense on surplus note		(63,922)	(62,207)	(57,473)
Net investment income		93,065	80,588	83,814
Equity Securities [Member]
Schedule of Net Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income, operating		1,509	1,632	1,751
Policy Loans and Other Invested Assets [Member]
Schedule of Net Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income, operating		1,046	1,019	1,244
Cash, Cash Equivalents and Short-Term Investments [Member]
Schedule of Net Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income, operating		5,943	456	1,202
Total return on deposit asset underlying 10% insurance agreement [Member]
Schedule of Net Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income, operating	[1]	(65)	1,875	4,253
Available-for-Sale [Member] | Fixed Maturities
Schedule of Net Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income, operating		90,975	80,362	82,805
Held-to-Maturity [Member] | Fixed Maturities
Schedule of Net Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income, operating		$ 63,922	$ 62,207	$ 57,473

[1] Includes $(3.8) million, $(2.5) million, and $2.0 million 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, 2022, 2021, and 2020, respectively.