Fair Value of Financial Instruments - Carrying Values and Estimated Fair Values of Financial Instruments (Details) - USD ($) $ in Thousands		Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale debt securities, at fair value		$ 2,719,467	$ 2,495,456
Fixed-maturity security held to maturity, fair value		1,334,892	1,340,265
Equity securities		29,680	35,404
Separate account assets		2,395,842	2,305,717
Surplus note		1,386,592	1,444,469
Separate account liabilities		2,395,842	2,305,717	$ 2,799,992
Fixed-maturity security (held-to-maturity)		1,386,980	1,444,920
Reported Value Measurement [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale debt securities, at fair value		2,719,467	2,495,456
Short-term investments (available-for-sale)		276	69,406
Equity securities		29,680	35,404
Trading securities		18,383	3,698
Separate account assets		2,395,842	2,305,717
Separate account liabilities		2,395,842	2,305,717
Reported Value Measurement [Member] | Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Policy loans	[1]	38,975	35,940
Surplus note	[1],[2]	1,386,592	1,444,469
Fixed-maturity security (held-to-maturity)	[1]	1,386,980	1,444,920
Reported Value Measurement [Member] | Level 3 [Member] | Deposits [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Deposit asset underlying 10% coinsurance agreement	[1]	187,377	224,371
Reported Value Measurement [Member] | Senior Notes [Member] | Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Notes payable - Long term	[2],[3]	593,709	592,905
Estimate of Fair Value Measurement [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale debt securities, at fair value		2,719,467	2,495,456
Short-term investments (available-for-sale)		276	69,406
Equity securities		29,680	35,404
Trading securities		18,383	3,698
Separate account assets		2,395,842	2,305,717
Separate account liabilities		2,395,842	2,305,717
Estimate of Fair Value Measurement [Member] | Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fixed-maturity security held to maturity, fair value	[1]	1,334,892	1,340,265
Policy loans	[1]	38,975	35,940
Surplus note	[1],[2]	1,329,159	1,333,047
Estimate of Fair Value Measurement [Member] | Level 3 [Member] | Deposits [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Deposit asset underlying 10% coinsurance agreement	[1]	187,377	224,371
Estimate of Fair Value Measurement [Member] | Senior Notes [Member] | Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Notes payable - Long term	[2],[3]	$ 508,832	$ 491,753

[1] Classified as level 3 fair value measurement

[2] Carrying value amounts shown are net of unamortized issuance costs.

[3] Classified as level 2 fair value measurement.