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Convertible Securities (Tables) | 12 Months Ended
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Dec. 31, 2014
Debt Disclosure [Abstract] |
Schedule of Carrying Value of Convertible Securities | The carrying values of the Company's convertible securities are as follows:
| December 31, 2013 |  | December 31, 2014
| Carrying Value |  | Principal amount at maturity |  | Carrying Value |  | Principal amount at maturity
Junior convertible securities: |  |  |  |  |  |  |
2007 junior convertible securities(1) | $ | 301.2 |  |  | $ | 430.8 |  |  | $ | 303.1 |  |  | $ | 430.8 |
2006 junior convertible securities | 217.5 |  |  | 300.0 |  |  | — |  |  | — |
Total junior convertible securities | $ | 518.7 |  |  | $ | 730.8 |  |  | $ | 303.1 |  |  | $ | 430.8 |
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(1) | The carrying value is accreted to the principal amount at maturity over a remaining life of 23 years.

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- Definition Tabular disclosure of the carrying amount and fair value of convertible securities. + References No definition available. + Details
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