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Indebtedness (Narrative) (Details) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Dec. 31, 2005 | Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021 | Dec. 31, 2004
Maximum borrowing percentage |  | 10.00% |  |  |
Debt Issuance Costs, Gross |  | $ 3,300 |  |  |
Net proceeds from the issuance |  | $ 20,000 | $ 60,000 | $ 0 |
Borrowing threshold of FHLBI |  | 20 |  |  |
Five Point Three Hundred Seventy Five Percent Senior Notes [Member] |  |  |  |  |
Original debt issuance |  | $ 300,000 |  |  |
Interest Rate |  | 5.375% |  |  |
Discount for notes issued |  | $ 5,900 |  |  |
Net proceeds from the issuance |  | 290,800 |  |  |
Five Point Eight Hundred Seventy Five Percent Senior Notes [Member] |  |  |  |  |
Original debt issuance |  | $ 185,000 |  |  |
Interest Rate |  | 5.875% |  |  |
Proceeds From Debt Issuance After Redemption |  | $ 106,000 |  |  |
Debt Retirement Costs Before Tax |  | 4,200 |  |  |
Debt Retirement Costs Net of Tax |  | 3,300 |  |  |
Three Point Zero Three Percent Borrowing From Federal Home Loan Bank Due December 16, 2026 [Member] |  |  |  |  |
Federal Home Loan Bank Advances |  |  | 45,000 |  |
Original debt issuance |  | $ 60,000 |  |  |
Interest Rate |  | 3.03% |  |  |
Net proceeds from the issuance |  |  | 15,000 |  |
Six Point Seventy Percent Senior Notes due 2035 [Member] |  |  |  |  |
Acceleration of principal |  | $ 10,000 |  |  |
Original debt issuance |  | $ 100,000 |  |  |
Interest Rate |  | 6.70% |  |  |
Discount for notes issued | $ 700 |  |  |  |
Net proceeds from the issuance | $ 50,000 |  |  |  |
Effective yield | 6.754% |  |  |  |
Seven Point Twenty Five Percent Senior Notes due 2034 [Member] |  |  |  |  |
Acceleration of principal |  | $ 10,000 |  |  |
Original debt issuance |  | $ 50,000 |  |  |
Interest Rate |  | 7.25% |  |  |
Discount for notes issued |  |  |  |  | $ 100
Effective yield |  |  |  |  | 7.27%
Bond proceeds to Insurance Subsidiaries as capital |  |  |  |  | $ 25,000
Line of Credit [Member] |  |  |  |  |
Acceleration of principal |  | $ 30,000 |  |  |
Maximum borrowing percentage |  | 10.00% |  |  |
Zero Point Seventy Percent Borrowing from FHLBNY Due June 27, 2022. [Member] | Selective Insurace Company of America (SICA) [Member] |  |  |  |  |
Federal Home Loan Bank Advances |  | $ 20,000 |  |  |
Federal Home Loan Bank, Advances, Interest Rate |  | 5.00% |  |  |
Federal Home Loan Bank of Indianapolis [Member] |  |  |  |  |
Aggregate investment in FHLBI |  | $ 5,200 | $ 5,200 |  |

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