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Shareholders' Equity (Details) - USD ($) $ / shares in Units, $ in Thousands | 1 Months Ended | 3 Months Ended | 12 Months Ended
--- | --- | --- | ---
Apr. 30, 2017 | Dec. 31, 2017 | Sep. 30, 2016 | Dec. 31, 2017 | Dec. 31, 2016
Debt Instrument [Line Items] |  |  |  |  |
Shares repurchased, weighted average price per share |  |  |  |  | $ 8.03
Shares repurchased, value |  |  |  |  | $ 147,100
Shareholder rights accompanying each outstanding share of the company's common stock (in number of Rights) |  | 1 |  | 1 |
Common stock, beneficial ownership threshold to be considered an Acquiring Person (in hundredths) |  | 5.00% |  | 5.00% |
Purchase price (in dollars per share) |  | $ 45 |  | $ 45 |
Purchase price (in dollars per one-tenth share) |  | 4.50 |  | 4.50 |
Redemption price (in dollars per Right) |  | $ 0.001 |  | $ 0.001 |
Rights |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Period after person becomes acquiring person |  |  |  | 10 days |
Common stock purchased per right |  | 0.1 |  | 0.1 |
2% Convertible Senior Notes due 2020 |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Principal amount of notes converted into shares | $ 202,500 |  |  |  |
Shares issued during period upon conversion of convertible debt (in shares) | 29,100,000 |  |  |  |
Treasury stock reissued during period upon conversion of notes (in shares) | 18,700,000 |  |  |  |
Stock issued during period upon conversion of notes, new issues (in shares) | 10,400,000 |  |  |  |
Repayments of debt (in shares) |  |  | 18,300,000 |  | 18,300,000
Stated interest rate (in hundredths) |  | 2.00% |  | 2.00% |
Convertible Junior Subordinated Debentures, at 9% per annum, Due 2063 |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Stated interest rate (in hundredths) |  | 9.00% |  | 9.00% |
Reacquisition of convertible junior subordinated debentures-equity component |  |  |  |  | $ 6,300
Accumulated other comprehensive loss |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Cumulative effect to reclassify certain tax effects from accumulated other comprehensive loss |  | $ (10,400) |  | $ (10,422) |
Retained earnings (deficit) |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Cumulative effect to reclassify certain tax effects from accumulated other comprehensive loss |  | $ 10,400 |  | $ 10,422 |

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- Definition The minimum percentage of beneficial ownership of the company's common stock by any person, by itself or together with its affiliates and associates, required to be considered an Acquiring Person as defined in the Shareholder Rights Agreement. + References No definition available. + Details
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