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Convertible Securities - Schedule of carrying amount and fair value of convertible notes (Details) (USD $) |  |  |  |  | 12 Months Ended |  |  |  |
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Dec. 31, 2013 | Dec. 31, 2012 | Dec. 31, 2013 2008 senior convertible notes [Member] | Dec. 31, 2012 2008 senior convertible notes [Member] | Dec. 31, 2013 Junior convertible trust preferred securities [Member] junior_note | Dec. 31, 2013 2007 junior convertible trust preferred securities [Member] | Dec. 31, 2012 2007 junior convertible trust preferred securities [Member] | Dec. 31, 2013 2006 junior convertible trust preferred securities [Member] | Dec. 31, 2012 2006 junior convertible trust preferred securities [Member]
Deb Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Repurchased face amount |  |  | $ 460,000,000 |  |  |  |  |  |  |  |  |  |  |  |
Interest rate |  |  | 3.95% |  |  |  |  | 5.15% | [1] |  |  | 5.10% | [2] |  |
Repurchase amount |  |  | 641,300,000 |  |  |  |  |  |  |  |  |  |  |  |
Number of securities outstanding |  |  |  |  |  |  | 2 |  |  |  |  |  |  |  |
Senior convertible securities, Carrying Value |  |  | 0 | [3] | 450,100,000 | [3] |  |  |  |  |  |  |  |  |
Junior convertible trust preferred securities, Carrying Value | 518,700,000 | 515,500,000 |  |  |  |  |  | 301,200,000 | [1],[3],[4] | 299,400,000 | [3] | 217,500,000 | [2],[3],[4] | 216,100,000 | [3]
Principal amount at maturity | $ 730,800,000 | $ 730,800,000 | $ 0 | [3] | $ 460,000,000 | [3] |  | $ 430,800,000 | [1],[3] | $ 430,800,000 | [3] | $ 300,000,000 | [2],[3] | $ 300,000,000 | [3]
Debt instrument term |  |  |  |  |  |  | 30 years |  |  |  |  |  |  |  |
[1] | 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.
[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] | 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] | 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.

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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 Carrying amount of senior long-term convertible debt as of the balance sheet date, net of the amount due in the next twelve months. The debt is convertible into a defined number of shares of common stock upon the occurrence of certain events. The holders may put these securities to the company. + References No definition available. + Details
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- Definition Face (par) amount of debt instrument at time of issuance. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28551-108399 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 55 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=6584090&loc=d3e28878-108400 + Details
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- Definition Contractual interest rate for funds borrowed, under the debt agreement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 22 -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22(a)(1)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition Period of time between issuance and maturity of debt instrument, 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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