| **Income Taxes**                     | 9 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  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| **Income Tax Disclosure [Abstract]** |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     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| Income Taxes                         | Income TaxesOur Provision for income tax expense of $42.1 million and $124.2 million for the three and nine months ended September 30, 2016, respectively, primarily resulted from the application of our estimated effective blended federal and state income tax rate. Our Provision for income tax expense of$35.9 million and $98.4 million for the three and nine months ended September 30, 2015, respectively, primarily resulted from the application of our estimated effective blended federal and state income tax rate.The $72.6 million of net deferred tax assets included in the accompanying condensed consolidated balance sheet as of September 30, 2016 reflects management’s assessment it is more likely than not we will be able to generate sufficient future taxable income to utilize those deferred tax assets based on our current estimates and assumptions. As of September 30, 2016, we maintained a valuation allowance of $28.3 million due to uncertainties regarding our ability to utilize a portion of our state net operating losses (“NOLs”) and other credits before they expire. The amount of the valuation allowance has been determined for each tax jurisdiction based on the weight of all available evidence including management’s estimates of taxable income for each jurisdiction in which we operate over the periods in which the related deferred tax assets will be recoverable. It is possible we may be required to increase or decrease our valuation allowance at some future time if our forecast of future earnings varies from actual results on a consolidated basis or in the applicable state tax jurisdictions, or if the timing of future tax deductions differs from our expectations.As of September 30, 2016, we estimate the tax benefit of combined federal NOLs and tax credits to be approximately $18 million. There is $15.6 million related to operating loss carryforwards resulting from excess tax benefits related to share-based awards, the benefits of which, when recognized, will be accounted for as a credit to Capital in excess of par value when they reduce taxes payable. Federal NOLs and tax credits expire in various amounts at varying times through 2036. We also have state NOLs that expire in various amounts at varying times through 2031.During the three months ended September 30, 2016, we filed an automatic tax accounting method change related to the deductibility of bad debts pursuant to the non-accrual experience method which resulted in a tax benefit of approximately $7 million. This change did not have a material impact on our effective tax rate. We also filed a non-automatic tax accounting method change related to billings denied under pre-payment claims reviews conducted by certain of our Medicare Administrative Contractors and are awaiting acceptance by the IRS. If our request for the non-automatic tax accounting method change is accepted as filed, we anticipate additional tax benefits of approximately $50 million through September 30, 2016. Approximately $44 million of this amount represents pre-payment claims received in years prior to and including the year ending December 31, 2015. This change, if approved, is not expected to have a material impact on our effective tax rate.Total remaining gross unrecognized tax benefits were $2.8 million and $2.9 million as of September 30, 2016 and December 31, 2015, respectively, all of which would affect our effective tax rate if recognized. A reconciliation of the beginning and ending liability for unrecognized tax benefits is as follows (in millions): Gross Unrecognized Income Tax BenefitsBalance at December 31, 2015$2.9Gross amount of increases in unrecognized tax benefits related to prior periods0.3Gross amount of decreases in unrecognized tax benefits related to prior periods(0.4)Gross amount of increases in unrecognized tax benefits related to current periods0.1Gross amount of decreases in unrecognized tax benefits related to current periods(0.1)Balance at September 30, 2016$2.8Our continuing practice is to recognize interest and penalties related to income tax matters in income tax expense. Interest recorded as part of our income tax provision during the three and nine months ended September 30, 2016 and 2015 was not material. Accrued interest income related to income taxes as of September 30, 2016 and December 31, 2015 was not material.In December 2014, we signed an agreement with the IRS to begin participating in their Compliance Assurance Process, a program in which we and the IRS endeavor to agree on the treatment of significant tax positions prior to the filing of our federal income tax return. We signed a new agreement in December 2015 for the 2016 tax year. As a result of these agreements, the IRS surveyed our 2013, 2012 and 2011 federal income tax returns, will examine our 2016 return when filed and is currently examining our 2015 return. Our 2014 federal income tax return has been filed, and the IRS has not indicated its intent to examine or survey this return. We have settled federal income tax examinations with the IRS for all tax years through 2013. Our state income tax returns are also periodically examined by various regulatory taxing authorities. We are currently under audit by five states for tax years ranging from 2007 through 2014.For the tax years that remain open under the applicable statutes of limitation, amounts related to unrecognized tax benefits have been considered by management in its estimate of our potential net recovery of prior years’ income taxes. Based on discussions with taxing authorities, we anticipate up to $2.6 million of our unrecognized tax benefits may be released within the next 12 months. |

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| - Definition
The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.
+ References
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