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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, 2020 | Sep. 30, 2020 | Jun. 30, 2020 | Mar. 31, 2020 | Dec. 31, 2019 | Sep. 30, 2019 | Jun. 30, 2019 | Mar. 31, 2019 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Basic earnings per share [Abstract] |  |  |  |  |  |  |  |  |  |  |
Net income | $ 151,430 | $ 130,811 | $ 14,047 | $ 149,805 | $ 177,110 | $ 176,934 | $ 167,778 | $ 151,941 | $ 446,093 | $ 673,763 | $ 670,097
Weighted average common shares outstanding - basic (in shares) |  |  |  |  |  |  |  |  | 339,953 | 352,827 | 365,406
Basic earnings per share (in dollars per share) | $ 0.45 | $ 0.39 | $ 0.04 | $ 0.44 | $ 0.51 | $ 0.50 | $ 0.47 | $ 0.43 | $ 1.31 | $ 1.91 | $ 1.83
Diluted earnings per share [Abstract] |  |  |  |  |  |  |  |  |  |  |
Net income | $ 151,430 | $ 130,811 | $ 14,047 | $ 149,805 | $ 177,110 | $ 176,934 | $ 167,778 | $ 151,941 | $ 446,093 | $ 673,763 | $ 670,097
Diluted income available to common shareholders |  |  |  |  |  |  |  |  | $ 463,097 | $ 692,027 | $ 688,361
Weighted-average shares - basic (in shares) |  |  |  |  |  |  |  |  | 339,953 | 352,827 | 365,406
Effect of dilutive securities [Abstract] |  |  |  |  |  |  |  |  |  |  |
Weighted-average shares - diluted (in shares) |  |  |  |  |  |  |  |  | 359,293 | 373,924 | 386,078
Diluted income per share (in dollars per share) | $ 0.44 | $ 0.38 | $ 0.04 | $ 0.42 | $ 0.49 | $ 0.49 | $ 0.46 | $ 0.42 | $ 1.29 | $ 1.85 | $ 1.78
Federal statutory income tax rate (in hundredths) |  |  |  |  |  |  |  |  | 21.00% | 21.00% | 21.00%
9% Convertible Junior Subordinated Debentures due 2063 |  |  |  |  |  |  |  |  |  |  |
Diluted earnings per share [Abstract] |  |  |  |  |  |  |  |  |  |  |
Dilutive securities |  |  |  |  |  |  |  |  | $ 17,004 | $ 18,264 | $ 18,264
Effect of dilutive securities [Abstract] |  |  |  |  |  |  |  |  |  |  |
Dilutive securities (in shares) |  |  |  |  |  |  |  |  | 17,751 | 19,028 | 19,028
Stated interest rate (in hundredths) | 9.00% |  |  |  | 9.00% |  |  |  | 9.00% | 9.00% | 9.00%
Unvested Restricted Stock Units |  |  |  |  |  |  |  |  |  |  |
Effect of dilutive securities [Abstract] |  |  |  |  |  |  |  |  |  |  |
Dilutive securities - Share based compensation (in shares) |  |  |  |  |  |  |  |  | 1,589 | 2,069 | 1,644

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