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Fair Value Measurements (Carrying Value and Estimated Fair Value of Financial Instruments) (Details) - USD ($) $ in Thousands | Dec. 31, 2020 | Dec. 31, 2019
--- | --- | ---
Fixed Income Securities, Available-for-sale, at fair value | $ 6,455,928 | $ 6,095,620
Equity securities | 310,367 | 72,937
Short-term investments | 409,852 | 282,490
Long-term debt | 550,743 | 550,597
Unamortized Debt Issuance Costs | (3,419) |
Finance Lease, Liability | 508 | 737
Seven Point Twenty Five Percent Senior Notes [Member] |  |
Long-term Debt, Fair Value | 66,148 | 66,365
Unamortized Debt Issuance Costs | (166) |
Six Point Seventy Percent Senior Notes [Member] |  |
Long-term Debt, Fair Value | 127,886 | 123,104
Unamortized Debt Issuance Costs | (319) |
Five Point Three Hundred Seventy Five [Member] |  |
Long-term Debt, Fair Value | 383,669 | 357,025
Unamortized Debt Issuance Costs | (2,934) |
One Point Sixty One Percent Borrowing From Federal Home Loan Bank Due July 21, 2021 [Member] |  |
Long-term Debt, Fair Value | 25,182 | 24,901
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 | 24,875
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 | 67,513 | 63,002
Unamortized Debt Issuance Costs | 0 |
Finance lease obligation [Member] |  |
Finance Lease, Liability | 508 | 737
Carrying Amount [Member] |  |
Long-term debt | 550,743 | 550,597
Carrying Amount [Member] | Seven Point Twenty Five Percent Senior Notes [Member] |  |
Long-term debt | 49,914 | 49,910
Carrying Amount [Member] | Six Point Seventy Percent Senior Notes [Member] |  |
Long-term debt | 99,499 | 99,480
Carrying Amount [Member] | Five Point Three Hundred Seventy Five [Member] |  |
Long-term debt | 294,241 | 294,157
Carrying Amount [Member] | One Point Sixty One Percent Borrowing From Federal Home Loan Bank Due July 21, 2021 [Member] |  |
Long-term debt | 25,000 | 25,000
Carrying Amount [Member] | One Point Fifty Six Percent Borrowing From Federal Home Loan Bank Due August 16, 2021 [Member] |  |
Long-term debt | 25,000 | 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 | 553,654 | 553,547
Carrying Amount [Member] | Unamortized Debt Issuance Costs [Member] |  |
Unamortized Debt Issuance Costs | (3,419) | (3,687)
Carrying Amount [Member] | Finance lease obligation [Member] |  |
Finance Lease, Liability | 508 | 737
Fair Value [Member] |  |
Long-term Debt, Fair Value | 695,596 | 659,272
Fair Value [Member] | Seven Point Twenty Five Percent Senior Notes [Member] |  |
Long-term Debt, Fair Value | 66,148 | 66,365
Fair Value [Member] | Six Point Seventy Percent Senior Notes [Member] |  |
Long-term Debt, Fair Value | 127,886 | 123,104
Fair Value [Member] | Five Point Three Hundred Seventy Five [Member] |  |
Long-term Debt, Fair Value | 383,669 | 357,025
Fair Value [Member] | One Point Sixty One Percent Borrowing From Federal Home Loan Bank Due July 21, 2021 [Member] |  |
Long-term Debt, Fair Value | 25,182 | 24,901
Fair Value [Member] | One Point Fifty Six Percent Borrowing From Federal Home Loan Bank Due August 16, 2021 [Member] |  |
Long-term Debt, Fair Value | 25,198 | 24,875
Fair Value [Member] | Three Point Zero Three Percent Borrowing From Federal Home Loan Bank Due December 16, 2026 [Member] |  |
Long-term Debt, Fair Value | $ 67,513 | $ 63,002

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