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Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2018 | Sep. 30, 2017 | Sep. 30, 2018 | Sep. 30, 2017
Basic earnings per share: |  |  |  |
Net income | $ 181,900 | $ 120,027 | $ 512,351 | $ 328,447
Weighted average common shares outstanding - basic (in shares) | 362,180 | 370,586 | 367,190 | 359,613
Basic earnings per share (in dollars per share) | $ 0.50 | $ 0.32 | $ 1.40 | $ 0.91
Diluted earnings per share: |  |  |  |
Net income | $ 181,900 | $ 120,027 | $ 512,351 | $ 328,447
Diluted income available to common shareholders | $ 186,466 | $ 123,784 | $ 526,049 | $ 342,333
Weighted average common shares outstanding - basic (in shares) | 362,180 | 370,586 | 367,190 | 359,613
Effect of dilutive securities: |  |  |  |
Weighted average common shares outstanding - diluted (in shares) | 382,905 | 391,087 | 387,765 | 395,870
Diluted earnings per share (in dollars per share) | $ 0.49 | $ 0.32 | $ 1.36 | $ 0.86
Effective income tax rate |  |  | 21.00% | 35.00%
2% Convertible Senior Notes |  |  |  |
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] |  |  |  |
Stated interest rate |  | 2.00% |  | 2.00%
Diluted earnings per share: |  |  |  |
Dilutive securities | $ 0 | $ 0 | $ 0 | $ 907
Effect of dilutive securities: |  |  |  |
Dilutive securities (in shares) | 0 | 0 | 0 | 11,119
5% Convertible Senior Notes |  |  |  |
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] |  |  |  |
Stated interest rate |  | 5.00% |  | 5.00%
Diluted earnings per share: |  |  |  |
Dilutive securities | $ 0 | $ 0 | $ 0 | $ 1,709
Effect of dilutive securities: |  |  |  |
Dilutive securities (in shares) | 0 | 0 | 0 | 4,743
9% Convertible Junior Subordinated Debentures |  |  |  |
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] |  |  |  |
Stated interest rate | 9.00% |  | 9.00% |
Diluted earnings per share: |  |  |  |
Dilutive securities | $ 4,566 | $ 3,757 | $ 13,698 | $ 11,270
Effect of dilutive securities: |  |  |  |
Dilutive securities (in shares) | 19,028 | 19,028 | 19,028 | 19,028
Unvested RSUs |  |  |  |
Effect of dilutive securities: |  |  |  |
Unvested RSUs (in shares) | 1,697 | 1,473 | 1,547 | 1,367

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