| **Fair Value Measurements (Tables)**                                          | 3 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |
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| **Fair Value Disclosures [Abstract]**                                         |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |
| Schedule of Fair Value, Assets and Liabilities Measured on a Recurring Basis  | Our financial assets and liabilities that are measured at fair value on a recurring basis are as follows (in millions):   Fair Value Measurements at Reporting Date UsingAs of March 31, 2013Fair Value Quoted Prices in Active Markets for Identical Assets(Level 1) Significant Other Observable Inputs(Level 2) Significant Unobservable Inputs(Level 3) Valuation Technique (1)Other current assets:         Current portion of restricted marketable securities$16.9 $— $16.9 $— MOther long-term assets:         Restricted marketable securities39.1 — 39.1 — MAs of December 31, 2012         Other current assets:         Current portion of restricted marketable securities$16.4 $— $16.4 $— MOther long-term assets:         Restricted marketable securities39.4 — 39.4 — M(1)The three valuation techniques are: market approach (M), cost approach (C), and income approach (I). |
| Schedule of Carrying Amounts and Estimated Fair Values, Financial Instruments | The carrying amounts and estimated fair values for all of our other financial instruments are presented in the following table (in millions): As of March 31, 2013 As of December 31, 2012 Carrying Amount Estimated Fair Value Carrying Amount Estimated Fair ValueLong-term debt:       Advances under revolving credit facility$122.0 $122.0 $— $—7.25% Senior Notes due 2018302.8 324.9 302.9 328.68.125% Senior Notes due 2020286.3 321.2 286.2 321.57.75% Senior Notes due 2022280.6 303.4 280.7 306.55.75% Senior Notes due 2024275.0 277.0 275.0 277.1Other notes payable42.3 42.3 36.8 36.8Financial commitments:       Letters of credit— 35.9 — 39.5                                                                                                                                                                                                                                                                                                                                                                                                                |

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| - Definition
Tabular disclosure of the carrying amounts and estimated fair values for the Company's financial instruments as of the balance sheet dates presented.
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No definition available.
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| - Definition
Tabular disclosure of assets and liabilities, including [financial] instruments measured at fair value that are classified in stockholders' equity, if any, that are measured at fair value on a recurring basis. The disclosures contemplated herein include the fair value measurements at the reporting date by the level within the fair value hierarchy in which the fair value measurements in their entirety fall, segregating fair value measurements using quoted prices in active markets for identical assets (Level 1), significant other observable inputs (Level 2), and significant unobservable inputs (Level 3).
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=7578670&loc=d3e19190-110258
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