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v3.25.4

Debt and Credit Arrangements (Narrative) (Details) - USD ($) |  | 1 Months Ended | 12 Months Ended
--- | --- | --- | ---
Aug. 21, 2025 | Jul. 31, 2023 | Dec. 31, 2025 | Dec. 31, 2024 | Dec. 31, 2023
Debt Instrument [Line Items] |  |  |  |  |
Proceeds from issuance of debt, net |  |  | $ 495,000,000 | $ 0 | $ 0
Repayments Of Debt |  |  | 61,800,000 | 0 | 0
Federal Home Loan Bank Stock |  |  | 6,100,000 | 6,100,000 |
Outstanding borrowings with FHLB |  |  | 0 | 0 |
Line of Credit Facility, Maximum Borrowing Capacity |  | $ 150,000,000.0 |  |  |
Outstanding borrowings under credit agreement |  |  | 0 | 0 |
Interest Expense Debt |  |  | 43,200,000 | 34,100,000 | $ 34,100,000
Collateralized Borrowing Program [Member] |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Securities Held As Collateral At Fair Value |  |  | 339,200,000 | 130,900,000 |
Unsecured Revolving Credit Facility [Member] |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Unsecured revolving credit facility term |  | 5 years |  |  |
Senior debentures maturing September 1, 2030 [Member] |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Aggregate principal amount |  |  | $ 300,000,000.0 | $ 300,000,000.0 |
Debt instrument interest rate |  |  | 2.50% | 2.50% |
Debt issuance date |  |  | Aug. 24, 2020 | Aug. 24, 2020 |
Maturity date |  |  | Sep. 01, 2030 | Sep. 01, 2030 |
Senior debentures maturing September 1, 2035 [Member] |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Aggregate principal amount | $ 500,000,000 |  |  |  |
Debt instrument interest rate | 5.50% |  |  |  |
Maturity date | Sep. 01, 2035 |  | Sep. 01, 2035 | Sep. 01, 2035 |
Proceeds from issuance of debt, net | $ 496,700,000 |  |  |  |
Senior debentures unsecured mature on October 15, 2025 [Member] |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Debt instrument interest rate | 7.625% |  |  |  |
Maturity date | Oct. 15, 2025 |  | Oct. 15, 2025 | Oct. 15, 2025 |
Repayments Of Debt | $ 61,800,000 |  |  |  |
Senior debentures unsecured mature on April 15, 2026 [Member] |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Aggregate principal amount |  |  | $ 375,000,000.0 | $ 375,000,000.0 |
Debt instrument interest rate |  |  | 4.50% | 4.50% |
Debt issuance date |  |  | Apr. 08, 2016 | Apr. 08, 2016 |
Maturity date |  |  | Apr. 15, 2026 | Apr. 15, 2026 |
8.207% Subordinated Debentures [Member] |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Aggregate principal amount |  |  | $ 50,100,000 | $ 50,100,000 |
Maturity date |  |  | Feb. 03, 2027 | Feb. 03, 2027 |
Interest rate of Series B Subordinated Deferrable Interest Debentures |  |  | 8.207% | 8.207% |

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- Definition Amount of borrowings as of the balance sheet date from the Federal Home Loan Bank, which are primarily used to cover shortages in the required reserve balance and liquidity shortages. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 942 -SubTopic 470 -Name Accounting Standards Codification -Section 45 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org/1943274/2147478878/942-470-45-1 + Details
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