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Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2016 | Sep. 30, 2016 | Jun. 30, 2016 | Mar. 31, 2016 | Dec. 31, 2015 | Sep. 30, 2015 | Jun. 30, 2015 | Mar. 31, 2015 | Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014
Earnings Per Share [Abstract] |  |  |  |  |  |  |  |  |  |  |
Participating securities (as shares) |  |  |  |  |  |  |  |  | 100 | 100 | 100
Basic earnings per share [Abstract] |  |  |  |  |  |  |  |  |  |  |
Net income | $ 107,487 | $ 56,618 | $ 109,221 | $ 69,191 | $ 102,418 | $ 822,852 | $ 113,654 | $ 133,076 | $ 342,517 | $ 1,172,000 | $ 251,949
Weighted average common shares outstanding - basic (in shares) |  |  |  |  |  |  |  |  | 342,890 | 339,552 | 338,523
Basic income per share (in dollars per share) | $ 0.31 | $ 0.16 | $ 0.32 | $ 0.20 | $ 0.30 | $ 2.42 | $ 0.33 | $ 0.39 | $ 1.00 | $ 3.45 | $ 0.74
Diluted earnings per share [Abstract] |  |  |  |  |  |  |  |  |  |  |
Net income | $ 107,487 | $ 56,618 | $ 109,221 | $ 69,191 | $ 102,418 | $ 822,852 | $ 113,654 | $ 133,076 | $ 342,517 | $ 1,172,000 | $ 251,949
Diluted income available to common shareholders |  |  |  |  |  |  |  |  | $ 370,883 | $ 1,214,942 | $ 264,146
Weighted-average shares - Basic (in shares) |  |  |  |  |  |  |  |  | 342,890 | 339,552 | 338,523
Effect of dilutive securities [Abstract] |  |  |  |  |  |  |  |  |  |  |
Weighted-average shares - Diluted (in shares) |  |  |  |  |  |  |  |  | 431,992 | 468,039 | 413,522
Diluted income per share (in dollars per share) | $ 0.28 | $ 0.14 | $ 0.26 | $ 0.17 | $ 0.24 | $ 1.78 | $ 0.28 | $ 0.32 | $ 0.86 | $ 2.60 | $ 0.64
Antidilutive securities (in shares) |  |  |  |  |  |  |  |  | 0 | 0 | 54,500
Federal statutory income tax rate (in hundredths) |  |  |  |  |  |  |  |  | 35.00% | 35.00% | 35.00%
2% Convertible Senior Notes due 2020 |  |  |  |  |  |  |  |  |  |  |
Diluted earnings per share [Abstract] |  |  |  |  |  |  |  |  |  |  |
Dilutive securities |  |  |  |  |  |  |  |  | $ 6,111 | $ 7,928 | $ 12,197
Effect of dilutive securities [Abstract] |  |  |  |  |  |  |  |  |  |  |
Dilutive securities (in shares) |  |  |  |  |  |  |  |  | 54,450 | 71,917 | 71,917
Stated interest rate (in hundredths) | 2.00% |  |  |  |  |  |  |  | 2.00% |  |
5% Convertible Senior Notes due 2017 |  |  |  |  |  |  |  |  |  |  |
Diluted earnings per share [Abstract] |  |  |  |  |  |  |  |  |  |  |
Dilutive securities |  |  |  |  |  |  |  |  | $ 6,362 | $ 12,228 | $ 0
Effect of dilutive securities [Abstract] |  |  |  |  |  |  |  |  |  |  |
Dilutive securities (in shares) |  |  |  |  |  |  |  |  | 13,107 | 25,603 | 0
Stated interest rate (in hundredths) | 5.00% |  |  |  |  |  |  |  | 5.00% |  |
9% Convertible Junior Subordinated Debentures due 2063 |  |  |  |  |  |  |  |  |  |  |
Diluted earnings per share [Abstract] |  |  |  |  |  |  |  |  |  |  |
Dilutive securities |  |  |  |  |  |  |  |  | $ 15,893 | $ 22,786 | $ 0
Effect of dilutive securities [Abstract] |  |  |  |  |  |  |  |  |  |  |
Dilutive securities (in shares) |  |  |  |  |  |  |  |  | 20,075 | 28,854 | 0
Stated interest rate (in hundredths) | 9.00% |  |  |  |  |  |  |  | 9.00% |  |
Unvested Restricted Stock Units |  |  |  |  |  |  |  |  |  |  |
Effect of dilutive securities [Abstract] |  |  |  |  |  |  |  |  |  |  |
Dilutive securities - Share based compensation (in shares) |  |  |  |  |  |  |  |  | 1,470 | 2,113 | 3,082

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