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Fair Value Measurements (Carrying Value and Estimated Fair Value of Financial Instruments) (Details) - USD ($) $ in Thousands | Dec. 31, 2016 | Dec. 31, 2015
--- | --- | ---
Held-to-maturity Securities | $ 101,556 | $ 201,354
Available-for-sale Securities, Debt Securities | 4,792,540 | 4,408,203
Equity securities, AFS | 146,753 | 207,051
Short-term investments | 221,701 | 194,819
Short-term debt | 0 | 60,000
Long-term debt | 438,667 | 328,192
Seven Point Twenty Five Percent Senior Notes [Member] |  |
Long-term Debt, Fair Value | 56,148 | 56,929
Six Point Seventy Percent Senior Notes [Member] |  |
Long-term Debt, Fair Value | 108,333 | 110,363
Five Point Eight Hundred Seventy Five [Member] |  |
Long-term Debt, Fair Value | 176,860 | 192,474
One Point Sixty One Percent Borrowing From Federal Home Loan Bank Due July 21, 2021 [Member] |  |
Long-term Debt, Fair Value | 24,286 |
One Point Fifty Six Percent Borrowing From Federal Home Loan Bank Due August 16, 2021 [Member] |  |
Long-term Debt, Fair Value | 24,219 |
Three Point Zero Three Percent Borrowing From Federal Home Loan Bank Due December 16, 2026 [Member] |  |
Long-term Debt, Fair Value | 59,313 |
Zero Point Sixty Three Percent Borrowing From Federal Home Loan Bank Due July 22, 2016 [Member] |  |
Short-term debt | 0 | 15,000
Short-term Debt fair value |  | 14,977
One Point Twenty Five Percent Borrowing From Federal Home Loan Bank [Member] |  |
Short-term debt | 0 | 45,000
Short-term Debt fair value |  | 45,083
Carrying Amount [Member] |  |
Held-to-maturity Securities | 101,556 | 201,354
Available-for-sale Securities, Debt Securities | 4,792,540 | 4,408,203
Equity securities, AFS | 146,753 | 207,051
Short-term investments | 221,701 | 194,819
Short-term debt | 0 | 60,000
Long-term debt | 438,667 | 328,192
Carrying Amount [Member] | Seven Point Twenty Five Percent Senior Notes [Member] |  |
Long-term debt | 49,901 | 49,898
Carrying Amount [Member] | Six Point Seventy Percent Senior Notes [Member] |  |
Long-term debt | 99,430 | 99,415
Carrying Amount [Member] | Five Point Eight Hundred Seventy Five [Member] |  |
Long-term debt | 185,000 | 185,000
Carrying Amount [Member] | One Point Sixty One Percent Borrowing From Federal Home Loan Bank Due July 21, 2021 [Member] |  |
Long-term debt | 25,000 | 0
Carrying Amount [Member] | One Point Fifty Six Percent Borrowing From Federal Home Loan Bank Due August 16, 2021 [Member] |  |
Long-term debt | 25,000 | 0
Carrying Amount [Member] | Three Point Zero Three Percent Borrowing From Federal Home Loan Bank Due December 16, 2026 [Member] |  |
Long-term debt | 60,000 | 0
Carrying Amount [Member] | Long Term Debt Excluding Issuance Costs [Member] |  |
Long-term debt | 444,331 | 334,313
Carrying Amount [Member] | Unamortized Debt Issuance Costs [Member] |  |
Unamortized Debt Issuance Costs Related to Long-Term Debt | (5,664) | (6,121)
Carrying Amount [Member] | Zero Point Sixty Three Percent Borrowing From Federal Home Loan Bank Due July 22, 2016 [Member] |  |
Short-term debt | 0 | 15,000
Carrying Amount [Member] | One Point Twenty Five Percent Borrowing From Federal Home Loan Bank [Member] |  |
Short-term debt | 0 | 45,000
Fair Value [Member] |  |
Held-to-maturity Securities | 105,211 | 209,544
Available-for-sale Securities, Debt Securities | 4,792,540 | 4,408,203
Equity securities, AFS | 146,753 | 207,051
Short-term investments | 221,701 | 194,819
Short-term Debt fair value | 0 | 60,060
Long-term Debt, Fair Value | 449,159 | 359,766
Fair Value [Member] | Seven Point Twenty Five Percent Senior Notes [Member] |  |
Long-term Debt, Fair Value | 56,148 | 56,929
Fair Value [Member] | Six Point Seventy Percent Senior Notes [Member] |  |
Long-term Debt, Fair Value | 108,333 | 110,363
Fair Value [Member] | Five Point Eight Hundred Seventy Five [Member] |  |
Long-term Debt, Fair Value | 176,860 | 192,474
Fair Value [Member] | One Point Sixty One Percent Borrowing From Federal Home Loan Bank Due July 21, 2021 [Member] |  |
Long-term Debt, Fair Value | 24,286 | 0
Fair Value [Member] | One Point Fifty Six Percent Borrowing From Federal Home Loan Bank Due August 16, 2021 [Member] |  |
Long-term Debt, Fair Value | 24,219 | 0
Fair Value [Member] | Three Point Zero Three Percent Borrowing From Federal Home Loan Bank Due December 16, 2026 [Member] |  |
Long-term Debt, Fair Value | 59,313 | 0
Fair Value [Member] | Zero Point Sixty Three Percent Borrowing From Federal Home Loan Bank Due July 22, 2016 [Member] |  |
Short-term Debt fair value | 0 | 14,977
Fair Value [Member] | One Point Twenty Five Percent Borrowing From Federal Home Loan Bank [Member] |  |
Short-term Debt fair value | $ 0 | $ 45,083

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