| **Convertible Perpetual Preferred Stock (Tables)**                          | 9 Months Ended                                                                                                                                                                                                                                                                                                                                                                          |
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| **Convertible Perpetual Preferred Stock [Abstract]**                        |                                                                                                                                                                                                                                                                                                                                                                                    |
| Summary of Activity, Convertible Perpetual Preferred Stock                  | The following is a summary of the activity related to our Convertible perpetual preferred stock from December 31, 2011 to September 30, 2012 (in millions, except share data): Number of Shares Outstanding AmountBalance as of December 31, 2011400,000 $387.4Repurchase of preferred stock(46,645) (45.2)Balance as of September 30, 2012353,355 $342.2 |
| Summary of Purchase Price Allocation, Convertible Perpetual Preferred Stock | The allocation of the purchase price is as follows (in millions):  Nine Months Ended  September 30, 2012Carrying value of shares repurchased $45.2Cumulative dividends paid as part of purchase price 0.5Excess paid in transaction 0.8  $46.5                                                                                             |

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| - Definition
Tabular disclosure of the convertible perpetual preferred stock purchase price allocation.
+ References
No definition available.
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| - Definition
Tabular disclosure of temporary equity. Temporary equity is a security with redemption features that are outside the control of the issuer, is not classified as an asset or liability in conformity with GAAP, and is not mandatorily redeemable. Includes any type of security that is redeemable at a fixed or determinable price or on a fixed or determinable date or dates, is redeemable at the option of the holder, or has conditions for redemption which are not solely within the control of the issuer. If convertible, the issuer does not control the actions or events necessary to issue the maximum number of shares that could be required to be delivered under the conversion option if the holder exercises the option to convert the stock to another class of equity. If the security is a warrant or a rights issue, the warrant or rights issue is considered to be temporary equity if the issuer cannot demonstrate that it would be able to deliver upon the exercise of the option by the holder in all cases. Includes stock with put option held by ESOP and stock redeemable by holder only in the event of a change in control of the issuer.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Emerging Issues Task Force (EITF) -Number D-98 -Paragraph 2,4,5,6 -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 Statement of Financial Accounting Standard (FAS) -Number 129 -Paragraph 2,3,4,5,6,7,8 -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 3: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Principles Board Opinion (APB) -Number 12 -Paragraph 10 -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 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 08 -Paragraph d -Article 4Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 28 -Article 5
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