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Fair Value of Financial Instruments (Estimated Fair Values Of Financial Instruments) (Details) - USD ($) $ in Thousands | Dec. 31, 2015 | Dec. 31, 2014
--- | --- | ---
Assets |  |
Investments | $ 2,880,003 |
Liabilities |  |
Options sold | 11,785 | $ 4,219
Liabilities fair value | 301,785 | 294,219
Level 2 [Member] |  |
Liabilities |  |
Liabilities fair value | 301,525 | 294,025
Secured Debt [Member] | Borrowings [Member] |  |
Liabilities |  |
Liabilities fair value | 140,000 | 140,000
Secured Debt [Member] | Borrowings [Member] | Level 2 [Member] |  |
Liabilities |  |
Liabilities fair value | 140,000 | 140,000
Unsecured Debt [Member] | Borrowings [Member] |  |
Liabilities |  |
Liabilities fair value | 150,000 | 150,000
Unsecured Debt [Member] | Borrowings [Member] | Level 2 [Member] |  |
Liabilities |  |
Liabilities fair value | 150,000 | 150,000
Equity Contract [Member] |  |
Liabilities |  |
Equity contracts | 11,525 | 4,025
Investments [Member] |  |
Assets |  |
Investments | 3,380,642 | 3,403,822
Secured Debt [Member] | Secured Debt [Member] | Borrowings [Member] | Level 2 [Member] |  |
Liabilities |  |
Liabilities fair value |  | 140,000
Other liabilities [Member] | Not Designated as Hedging Instrument [Member] | Equity Contract [Member] |  |
Liabilities |  |
Options sold | $ 260 | $ 194

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