| **Fair Value Measurements**           | 3 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |
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| **Fair Value Disclosures [Abstract]** |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            |
| Fair Value Measurements               | Fair Value MeasurementsOur 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, 2014Fair 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$3.0 $— $3.0 $— MOther long-term assets:         Restricted marketable securities45.6 — 45.6 — MAs of December 31, 2013         Other current assets:         Current portion of restricted marketable securities$4.7 $— $4.7 $— MOther long-term assets:         Restricted marketable securities42.9 — 42.9 — M(1)  The three valuation techniques are: market approach (M), cost approach (C), and income approach (I).In addition to assets and liabilities recorded at fair value on a recurring basis, we are also required to record assets and liabilities at fair value on a nonrecurring basis. Generally, assets are recorded at fair value on a nonrecurring basis as a result of impairment charges or similar adjustments made to the carrying value of the applicable assets. During the three months ended March 31, 2014 and March 31, 2013, we did not record any material gains or losses related to our nonfinancial assets and liabilities that are recognized or disclosed at fair value in the financial statements on a nonrecurring basis as part of our continuing operations.As discussed in Note 1, Summary of Significant Accounting Policies, “Fair Value Measurements,” to the consolidated financial statements accompanying the 2013 Form 10-K, the carrying value equals fair value for our financial instruments that are not included in the table below and are classified as current in our condensed consolidated balance sheets. 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, 2014 As of December 31, 2013 Carrying Amount Estimated Fair Value Carrying Amount Estimated Fair ValueLong-term debt:       Advances under revolving credit facility$43.0 $43.0 $45.0 $45.07.25% Senior Notes due 2018272.4 288.0 272.4 291.48.125% Senior Notes due 2020286.7 315.0 286.6 319.47.75% Senior Notes due 2022252.5 276.2 252.5 275.05.75% Senior Notes due 2024275.0 282.6 275.0 273.62.00% Convertible Senior Subordinated Notes due 2043251.6 349.0 249.5 339.7Other notes payable46.3 46.3 47.6 47.6Financial commitments:       Letters of credit— 37.3 — 36.5Fair values for our long-term debt and financial commitments are determined using inputs, including quoted prices in nonactive markets, that are observable either directly or indirectly, or Level 2 inputs within the fair value hierarchy. See Note 1, Summary of Significant Accounting Policies, “Fair Value Measurements,” to the consolidated financial statements accompanying the 2013 Form 10-K. See also Note 3, Redeemable Noncontrolling Interests. |

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| - Definition
The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.
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