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Convertible Securities (Details) (USD $) | 6 Months Ended |
--- | --- | ---
Jun. 30, 2012 security | Dec. 31, 2011
Convertible Securities |  |
Carrying Value | $ 442,800,000 | $ 435,600,000
Carrying Value | 514,000,000 | 512,600,000
Principal amount at maturity | 730,800,000 | 730,800,000
Principal terms of Convertible Debt Securities |  |
Deferred tax liabilities | 24,500,000 |
2008 senior convertible notes |  |
Debt |  |
Number of securities outstanding | 1 |
Convertible Securities |  |
Carrying Value | 442,800,000 | 435,600,000
Principal amount at maturity | 460,000,000 | 460,000,000
Term of debt (in years) | 5 years |
Principal terms of Convertible Debt Securities |  |
Denomination | 1,000 |
Current conversion rate | 7.959 |
Current conversion price (in dollars per share) | $ 125.65 |
Stated coupon (as a percent) | 3.95% |
Tax deduction rate (as a percent) | 9.38% |
Junior convertible trust preferred securities |  |
Debt |  |
Number of securities outstanding | 2 |
2007 junior convertible trust preferred securities |  |
Convertible Securities |  |
Carrying Value | 298,600,000 | 297,800,000
Principal amount at maturity | 430,800,000 | 430,800,000
Term of debt (in years) | 30 years |
Principal terms of Convertible Debt Securities |  |
Denomination | 50 |
Current conversion rate | 0.250 |
Current conversion price (in dollars per share) | $ 200.00 |
Stated coupon (as a percent) | 5.15% |
Tax deduction rate (as a percent) | 8.00% |
Minimum stock price for convertible notes to be redeemed (in dollars per share) | $ 260 |
2006 junior convertible trust preferred securities |  |
Convertible Securities |  |
Carrying Value | 215,400,000 | 214,800,000
Principal amount at maturity | 300,000,000 | 300,000,000
Term of debt (in years) | 30 years |
Principal terms of Convertible Debt Securities |  |
Denomination | $ 50 |
Current conversion rate | 0.333 |
Current conversion price (in dollars per share) | $ 150.00 |
Stated coupon (as a percent) | 5.10% |
Tax deduction rate (as a percent) | 7.50% |
Minimum stock price for convertible notes to be redeemed (in dollars per share) | $ 195 |

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- Definition This element represents the minimum stock price that must be exceeded for the exchangeable notes to be exchanged by debt holders. + References No definition available. + Details
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- Definition Represents the denomination of the principal amount of debt used to determine the number of shares the debt can be converted into at the exchange rate. + References No definition available. + Details
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- Definition Represents the deferred taxes generated from the excess of the interest expense calculated under federal income tax regulations over interest expense as calculated for book purposes. + References No definition available. + Details
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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 The stated principal amount of the debt instrument at time of issuance, which may vary from the carrying amount because of unamortized premium or discount. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Principles Board Opinion (APB) -Number 21 -Paragraph 16, 20 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 2: 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 3: 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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