Fair Value of Financial Instruments - Carrying Values and Estimated Fair Values of Financial Instruments (Details) - USD ($) $ in Thousands		Jun. 30, 2024	Dec. 31, 2023	Dec. 31, 2022
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale debt securities, at fair value		$ 2,796,030	$ 2,719,467
Fixed-maturity security held to maturity, fair value		1,268,174	1,334,892
Equity securities		26,026	29,680
Separate account assets		2,253,966	2,395,842
Surplus note		1,353,014	1,386,592
Separate account liabilities		2,253,966	2,395,842	$ 2,305,717
Fixed-maturity security (held-to-maturity)		1,353,370	1,386,980
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		2,796,030	2,719,467
Short-term investments (available-for-sale)			276
Equity securities		26,026	29,680
Trading securities		3,158	18,383
Separate account assets		2,253,966	2,395,842
Separate account liabilities		2,253,966	2,395,842
Reported Value Measurement [Member] | Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Policy loans	[1]	38,426	38,975
Surplus note	[1],[2]	1,353,014	1,386,592
Fixed-maturity security (held-to-maturity)	[1]	1,353,370	1,386,980
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]	171,848	187,377
Reported Value Measurement [Member] | Level 2 [Member] | Senior Notes [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Note payable - Long term	[2],[3]	594,110	593,709
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		2,796,030	2,719,467
Short-term investments (available-for-sale)			276
Equity securities		26,026	29,680
Trading securities		3,158	18,383
Separate account assets		2,253,966	2,395,842
Separate account liabilities		2,253,966	2,395,842
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]	1,268,174	1,334,892
Policy loans	[1]	38,426	38,975
Surplus note	[1],[2]	1,265,532	1,329,159
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]	171,848	187,377
Estimate of Fair Value Measurement [Member] | Level 2 [Member] | Senior Notes [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Note payable - Long term	[2],[3]	$ 499,658	$ 508,832

[1] Classified as a Level 3 fair value measurement.

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

[3] Classified as a Level 2 fair value measurement.