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Fair Value Measurements (Carrying Value and Estimated Fair Value of Financial Instruments) (Details) - USD ($) $ in Thousands | Sep. 30, 2016 | Dec. 31, 2015
--- | --- | ---
Held-to-maturity securities | $ 130,472 | $ 201,354
Available-for-sale securities | 4,832,532 | 4,408,203
Equity securities, AFS | 147,304 | 207,051
Short-term investments | 169,604 | 194,819
Short-term debt | 45,000 | 60,000
Long-term debt | 378,551 | 328,192
Seven Point Twenty Five Percent Senior Notes [Member] |  |
Long-term debt | 60,682 | 56,929
Six Point Seventy Percent Senior Notes [Member] |  |
Long-term debt | 118,192 | 110,363
Five Point Eight Hundred Seventy Five Senior Notes [Member] |  |
Long-term debt | 194,324 | 192,474
One Point Sixty One Percent Borrowing From Federal Home Loan Bank Due July 21, 2021 [Member] |  |
Long-term debt | 25,048 |
One Point Fifty Six Percent Borrowing From Federal Home Loan Bank Due August 16, 2021 [Member] |  |
Long-term debt | 24,990 |
Zero Point Sixty Three Percent Borrowing From Federal Home Loan Bank Due July 22, 2016 [Member] |  |
Short-term debt |  | 14,977
One Point Twenty Five Percent Borrowing From Federal Home Loan Bank [Member] |  |
Short-term debt | 45,072 | 45,083
Reported Value Measurement [Member] |  |
Held-to-maturity securities | 130,472 | 201,354
Available-for-sale securities | 4,832,532 | 4,408,203
Equity securities, AFS | 147,304 | 207,051
Short-term investments | 169,604 | 194,819
Short-term debt | 45,000 | 60,000
Long-term debt | 378,551 | 328,192
Reported Value Measurement [Member] | Seven Point Twenty Five Percent Senior Notes [Member] |  |
Long-term debt | 49,900 | 49,898
Reported Value Measurement [Member] | Six Point Seventy Percent Senior Notes [Member] |  |
Long-term debt | 99,426 | 99,415
Reported Value Measurement [Member] | Five Point Eight Hundred Seventy Five Senior Notes [Member] |  |
Long-term debt | 185,000 | 185,000
Reported Value Measurement [Member] | One Point Sixty One Percent Borrowing From Federal Home Loan Bank Due July 21, 2021 [Member] |  |
Long-term debt | 25,000 | 0
Reported Value Measurement [Member] | One Point Fifty Six Percent Borrowing From Federal Home Loan Bank Due August 16, 2021 [Member] |  |
Long-term debt | 25,000 | 0
Reported Value Measurement [Member] | Long Term Debt Excluding Issuance Costs [Member] |  |
Long-term debt | 384,326 | 334,313
Reported Value Measurement [Member] | Unamortized Debt Issuance Costs [Member] |  |
Unamortized debt issuance costs | (5,775) | (6,121)
Reported Value Measurement [Member] | Zero Point Sixty Three Percent Borrowing From Federal Home Loan Bank Due July 22, 2016 [Member] |  |
Short-term debt | 0 | 15,000
Reported Value Measurement [Member] | One Point Twenty Five Percent Borrowing From Federal Home Loan Bank [Member] |  |
Short-term debt | 45,000 | 45,000
Estimate of Fair Value Measurement [Member] |  |
Held-to-maturity securities | 136,094 | 209,544
Available-for-sale securities | 4,832,532 | 4,408,203
Equity securities, AFS | 147,304 | 207,051
Short-term investments | 169,604 | 194,819
Short-term debt | 45,072 | 60,060
Long-term debt | 423,236 | 359,766
Estimate of Fair Value Measurement [Member] | Seven Point Twenty Five Percent Senior Notes [Member] |  |
Long-term debt | 60,682 | 56,929
Estimate of Fair Value Measurement [Member] | Six Point Seventy Percent Senior Notes [Member] |  |
Long-term debt | 118,192 | 110,363
Estimate of Fair Value Measurement [Member] | Five Point Eight Hundred Seventy Five Senior Notes [Member] |  |
Long-term debt | 194,324 | 192,474
Estimate of Fair Value Measurement [Member] | One Point Sixty One Percent Borrowing From Federal Home Loan Bank Due July 21, 2021 [Member] |  |
Long-term debt | 25,048 | 0
Estimate of Fair Value Measurement [Member] | One Point Fifty Six Percent Borrowing From Federal Home Loan Bank Due August 16, 2021 [Member] |  |
Long-term debt | 24,990 | 0
Estimate of Fair Value Measurement [Member] | Zero Point Sixty Three Percent Borrowing From Federal Home Loan Bank Due July 22, 2016 [Member] |  |
Short-term debt | 0 | 14,977
Estimate of Fair Value Measurement [Member] | One Point Twenty Five Percent Borrowing From Federal Home Loan Bank [Member] |  |
Short-term debt | $ 45,072 | $ 45,083

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