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Fair Value Measurements (Carrying Value and Estimated Fair Value of Financial Instruments) (Details) - USD ($) $ in Thousands | Sep. 30, 2015 | Dec. 31, 2014
--- | --- | ---
Carrying Amount [Member] |  |
Held-to-maturity Securities | $ 229,869 | $ 318,137
Available-for-sale Securities | 4,351,046 | 4,066,122
Equity securities, AFS | 221,951 | 191,400
Short-term investments | 125,855 | 131,972
Notes payable | 394,309 | 379,297
Carrying Amount [Member] | Zero Point Sixty Three Percent Borrowing From Federal Home Loan Bank Due July 22, 2016 [Member] |  |
Notes payable | 15,000 | 0
Carrying Amount [Member] | One Point Twenty Five Percent Borrowing From Federal Home Loan Bank [Member] |  |
Notes payable | 45,000 | 45,000
Carrying Amount [Member] | Seven Point Twenty Five Percent Senior Notes [Member] |  |
Notes payable | 49,898 | 49,896
Carrying Amount [Member] | Six Point Seventy Percent Senior Notes [Member] |  |
Notes payable | 99,411 | 99,401
Carrying Amount [Member] | Five Point Eight Hundred Seventy Five Senior Notes [Member] |  |
Notes payable | 185,000 | 185,000
Fair Value [Member] |  |
Held-to-maturity Securities | 240,388 | 333,961
Available-for-sale Securities | 4,351,046 | 4,066,122
Equity securities, AFS | 221,951 | 191,400
Short-term investments | 125,855 | 131,972
Notes payable | 418,548 | 404,270
Fair Value [Member] | Zero Point Sixty Three Percent Borrowing From Federal Home Loan Bank Due July 22, 2016 [Member] |  |
Notes payable | 14,995 | 0
Fair Value [Member] | One Point Twenty Five Percent Borrowing From Federal Home Loan Bank [Member] |  |
Notes payable | 45,277 | 45,244
Fair Value [Member] | Seven Point Twenty Five Percent Senior Notes [Member] |  |
Notes payable | 57,929 | 59,181
Fair Value [Member] | Six Point Seventy Percent Senior Notes [Member] |  |
Notes payable | 112,387 | 114,845
Fair Value [Member] | Five Point Eight Hundred Seventy Five Senior Notes [Member] |  |
Notes payable | $ 187,960 | $ 185,000

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