Fair Value of Financial Instruments - Carrying Values and Estimated Fair Values of Financial Instruments (Details) - USD ($) $ in Thousands |
Mar. 31, 2026 |
Dec. 31, 2025 |
Dec. 31, 2024 |
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| Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] | |||||||||||
| Available-for-sale debt securities, at fair value | $ 3,444,026 | $ 3,265,246 | |||||||||
| Fixed-maturity security held to maturity, fair value | 1,099,850 | 1,153,047 | |||||||||
| Equity securities | 27,728 | 26,433 | |||||||||
| Separate account assets | 2,122,558 | 2,281,520 | |||||||||
| Surplus note | 1,130,485 | 1,175,119 | |||||||||
| Separate account liabilities | 2,122,558 | 2,281,520 | $ 2,209,287 | ||||||||
| Fixed-maturity security (held-to-maturity) | 1,130,730 | 1,175,380 | |||||||||
| 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 | 3,444,026 | 3,265,246 | |||||||||
| Equity securities | 27,728 | 26,433 | |||||||||
| Trading securities | 32,451 | 12,801 | |||||||||
| Separate account assets | 2,122,558 | 2,281,520 | |||||||||
| Separate account liabilities | 2,122,558 | 2,281,520 | |||||||||
| Reported Value Measurement [Member] | Level 3 [Member] | |||||||||||
| Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] | |||||||||||
| Policy loans | [1] | 47,967 | 47,583 | ||||||||
| Surplus note | [1],[2] | 1,130,485 | 1,175,119 | ||||||||
| Fixed-maturity security (held-to-maturity) | [1] | 1,130,730 | 1,175,380 | ||||||||
| 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],[3] | 0 | 131,418 | ||||||||
| 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],[4] | 595,516 | 595,315 | ||||||||
| 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 | 3,444,026 | 3,265,246 | |||||||||
| Equity securities | 27,728 | 26,433 | |||||||||
| Trading securities | 32,451 | 12,801 | |||||||||
| Separate account assets | 2,122,558 | 2,281,520 | |||||||||
| Separate account liabilities | 2,122,558 | 2,281,520 | |||||||||
| 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] | 1,099,850 | 1,153,047 | ||||||||
| Policy loans | [1] | 47,967 | 47,583 | ||||||||
| Surplus note | [1],[2] | 1,097,767 | 1,150,995 | ||||||||
| 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],[3] | 0 | 131,418 | ||||||||
| 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],[4] | $ 536,267 | $ 543,461 | ||||||||
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