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Convertible Securities- Schedule of principal terms of convertible notes (Details) (USD $) | 12 Months Ended |
--- | --- | ---
Dec. 31, 2013 | Dec. 31, 2012
Debt Instrument [Line Items] |  |  |  |
Par value | $ 730,800,000 |  | $ 730,800,000 |
Junior convertible trust preferred securities, Carrying Value | 518,700,000 |  | 515,500,000 |
Deferred tax liability from excess interest expense calculation | 12,900,000 |  |  |
Junior convertible trust preferred securities [Member] |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Debt instrument term | 30 years |  |  |
2006 Junior Convertible Trust Preferred Securities [Member] |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Par value | 300,000,000 | [1],[2] | 300,000,000 | [1]
Junior convertible trust preferred securities, Carrying Value | 217,500,000 | [1],[2],[3] | 216,100,000 | [1]
Denomination | 50 | [2] |  |
Current conversion rate | 0.333 | [2] |  |
Current conversion price | $ 150.00 | [2] |  |
Stated coupon | 5.10% | [2] |  |
Tax deduction rate(4) | 7.50% | [2],[4] |  |
Redemption of debt | 8,100,000 |  |  |
2007 Junior Convertible Trust Preferred Securities [Member] |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Par value | 430,800,000 | [1],[5] | 430,800,000 | [1]
Junior convertible trust preferred securities, Carrying Value | 301,200,000 | [1],[3],[5] | 299,400,000 | [1]
Denomination | 50 | [5] |  |
Current conversion rate | 0.250 | [5] |  |
Current conversion price | $ 200.00 | [5] |  |
Stated coupon | 5.15% | [5] |  |
Tax deduction rate(4) | 8.00% | [4],[5] |  |
Price per share that must be exceeded for conversion | $ 260 |  |  |
Trading days | 20 |  |  |
Consecutive trading days | 30 days |  |  |
2008 senior convertible notes [Member] |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Par value | 0 | [1] | 460,000,000 | [1]
Stated coupon | 3.95% |  |  |
Deferred tax liability from excess interest expense calculation reclassified to stockholders' equity | $ 50,600,000 |  |  |
[1] | Carrying value is accreted to the principal amount at maturity over an expected life of 30 years for each of the junior convertible trust preferred securities.
[2] | On February 13, 2014, we delivered a notice to redeem all of our outstanding 2006 convertible trust preferred securities. In lieu of redemption, holders of the 2006 junior convertible trust preferred securities may elect to convert their securities into a defined number of shares. Upon conversion, holders will receive cash or shares of our common stock, or a combination thereof, at our election.
[3] | The carrying value is accreted to the principal amount at maturity over an expected life of 30 years for each of the junior convertible trust preferred securities.
[4] | These convertible securities are considered contingent payment debt instruments under federal income tax regulations, which require the Company to deduct interest in an amount greater than its reported Interest expense. These deductions result in annual deferred tax liabilities of approximately $12.9 million ($8.1 million assuming the redemption of the 2006 convertible trust preferred securities). These deferred tax liabilities will be reclassified directly to stockholders' equity if the Company's common stock is trading above certain thresholds at the time of the conversion of the securities. In 2013 , $50.6 million was reclassified to stockholders' equity related to the repurchase of the 2008 senior convertible notes.
[5] | The Company may redeem the 2007 junior convertible trust preferred securities if the closing price of the Company's common stock exceeds $260 per share for 20 trading days in a period of 30 consecutive trading days.

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- Definition Carrying amount of junior long-term convertible debt as of the balance sheet date, net of the amount due in the next twelve months. The debt is convertible, at any time, into a defined number of shares of common stock. Holders of the junior convertible trust preferred securities have no rights to put these securities. + References No definition available. + Details
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- Definition Threshold period of specified consecutive trading days within which common stock price to conversion price of convertible debt instruments must exceed threshold percentage for a specified number of trading days to trigger conversion feature, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References No definition available. + Details
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