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Fair Value Measurements (Carrying Value and Estimated Fair Value of Financial Instruments) (Details) - USD ($) $ in Thousands | Dec. 31, 2021 | Dec. 31, 2020
--- | --- | ---
Fixed Income Securities, Available-for-sale, at fair value | $ 6,709,976 | $ 6,455,928
Equity securities | 335,537 | 310,367
Short-term investments | 447,863 | 409,852
Long-term debt | 506,050 | 550,743
Unamortized Debt Issuance Costs | (3,167) |
Finance Lease, Liability | 5,450 | 508
Seven Point Twenty Five Percent Senior Notes [Member] |  |
Long-term Debt, Fair Value | 63,719 | 66,148
Unamortized Debt Issuance Costs | (147) |
Six Point Seventy Percent Senior Notes [Member] |  |
Long-term Debt, Fair Value | 127,574 | 127,886
Unamortized Debt Issuance Costs | (287) |
Five Point Three Hundred Seventy Five Percent Senior Notes [Member] |  |
Long-term Debt, Fair Value | 395,652 | 383,669
Unamortized Debt Issuance Costs | (2,733) |
One Point Sixty One Percent Borrowing From Federal Home Loan Bank Due July 21, 2021 [Member] |  |
Long-term Debt, Fair Value |  | 25,182
Unamortized Debt Issuance Costs | 0 |
One Point Fifty Six Percent Borrowing From Federal Home Loan Bank Due August 16, 2021 [Member] |  |
Long-term Debt, Fair Value |  | 25,198
Unamortized Debt Issuance Costs | 0 |
Three Point Zero Three Percent Borrowing From Federal Home Loan Bank Due December 16, 2026 [Member] |  |
Long-term Debt, Fair Value | 64,126 | 67,513
Unamortized Debt Issuance Costs | 0 |
Finance lease obligation [Member] |  |
Finance Lease, Liability | 5,450 | 508
Carrying Amount [Member] |  |
Long-term debt | 506,050 | 550,743
Carrying Amount [Member] | Seven Point Twenty Five Percent Senior Notes [Member] |  |
Long-term debt | 49,917 | 49,914
Carrying Amount [Member] | Six Point Seventy Percent Senior Notes [Member] |  |
Long-term debt | 99,520 | 99,499
Carrying Amount [Member] | Five Point Three Hundred Seventy Five Percent Senior Notes [Member] |  |
Long-term debt | 294,330 | 294,241
Carrying Amount [Member] | One Point Sixty One Percent Borrowing From Federal Home Loan Bank Due July 21, 2021 [Member] |  |
Long-term debt | 0 | 25,000
Carrying Amount [Member] | One Point Fifty Six Percent Borrowing From Federal Home Loan Bank Due August 16, 2021 [Member] |  |
Long-term debt | 0 | 25,000
Carrying Amount [Member] | Three Point Zero Three Percent Borrowing From Federal Home Loan Bank Due December 16, 2026 [Member] |  |
Long-term debt | 60,000 | 60,000
Carrying Amount [Member] | Long Term Debt Excluding Issuance Costs [Member] |  |
Long-term debt | 503,767 | 553,654
Carrying Amount [Member] | Unamortized Debt Issuance Costs [Member] |  |
Unamortized Debt Issuance Costs | (3,167) | (3,419)
Carrying Amount [Member] | Finance lease obligation [Member] |  |
Finance Lease, Liability | 5,450 | 508
Fair Value [Member] |  |
Long-term Debt, Fair Value | 651,071 | 695,596
Fair Value [Member] | Seven Point Twenty Five Percent Senior Notes [Member] |  |
Long-term Debt, Fair Value | 63,719 | 66,148
Fair Value [Member] | Six Point Seventy Percent Senior Notes [Member] |  |
Long-term Debt, Fair Value | 127,574 | 127,886
Fair Value [Member] | Five Point Three Hundred Seventy Five Percent Senior Notes [Member] |  |
Long-term Debt, Fair Value | 395,652 | 383,669
Fair Value [Member] | One Point Sixty One Percent Borrowing From Federal Home Loan Bank Due July 21, 2021 [Member] |  |
Long-term Debt, Fair Value | 0 | 25,182
Fair Value [Member] | One Point Fifty Six Percent Borrowing From Federal Home Loan Bank Due August 16, 2021 [Member] |  |
Long-term Debt, Fair Value | 0 | 25,198
Fair Value [Member] | Three Point Zero Three Percent Borrowing From Federal Home Loan Bank Due December 16, 2026 [Member] |  |
Long-term Debt, Fair Value | $ 64,126 | $ 67,513

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