Fair Value of Financial Instruments - Carrying Values and Estimated Fair Values of Financial Instruments (Details) - USD ($) $ in Thousands		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		$ 2,495,456	$ 2,702,567
Equity securities		35,404	42,551
Separate account assets		2,305,717	2,799,992
Surplus note		1,444,469	1,378,585
Separate account liabilities		2,305,717	2,799,992
Fixed-maturity security (held-to-maturity)		1,444,920	1,379,100
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		2,495,456	2,702,567
Short-term investments (available-for-sale)		69,406	85,243
Equity securities		35,404	42,551
Trading securities		3,698	24,355
Separate account assets		2,305,717	2,799,992
Separate account liabilities		2,305,717	2,799,992
Reported Value Measurement [Member] | Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Policy loans	[1]	35,940	30,612
Surplus note	[1],[2]	1,444,469	1,378,585
Fixed-maturity security (held-to-maturity)	[1]	1,444,920	1,379,100
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]	224,371	231,368
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]	592,905	592,102
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		2,495,456	2,702,567
Short-term investments (available-for-sale)		69,406	85,243
Equity securities		35,404	42,551
Trading securities		3,698	24,355
Separate account assets		2,305,717	2,799,992
Separate account liabilities		2,305,717	2,799,992
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]	1,340,265	1,551,113
Policy loans	[1]	35,940	30,612
Surplus note	[1],[2]	1,333,047	1,545,854
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]	224,371	231,368
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]	$ 491,753	$ 605,667

[1] Classified as level 3 fair value measurement.

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

[3] Classified as level 2 fair value measurement.