Organization, Consolidation and Presentation of Financial Statements [Abstract] Funds Receivable/Payable for the Benefit of Members [Table] Funds Receivable/Payable for the Benefit of Members [Table] Disclosure of accounting policy for Funds Receivable or Payable for the Benefit of Members [Table] Balance Sheet Location [Axis] Balance Sheet Location [Axis] Balance Sheet Location [Domain] Balance Sheet Location [Domain] Premiums receivable, net Premiums Receivable [Member] Counterparty Name [Axis] Counterparty Name [Axis] Counterparty Name [Domain] Counterparty Name [Domain] State Partners State Partners [Member] State Partners [Member] Medicare Advantage and PDP Medicare Advantage and PDP [Member] Medicare Advantage and PDP [Member] Segments [Axis] Segments [Axis] Segments [Domain] Segments [Domain] Medicaid Health Plans Medicaid [Member] A reportable segment and business line which includes plans for beneficiaries of various Medicaid programs and state-based programs that are not a part of the Medicaid program. Medicare Advantage Medicare Advantage [Member] A reportable segment within the Medicare business line which consists of Medicare Advantage coordinated care plans. Advance Payment CMS [Axis] Advance Payment CMS [Axis] Advance Payment reflected in Funds payable for the benefit of members. [Axis] Advance Payment CMS [Domain] Advance Payment CMS [Domain] [Domain] for Advance Payment reflected in Funds payable for the benefit of members. [Axis] Advance Payment CMS Advance Payment CMS [Member] Advance Payment CMS [Member] Funds Receivable/Payable for the Benefit of Members [Line Items] Funds Receivable/Payable for the Benefit of Members [Line Items] [Line Items] for Disclosure of accounting policy for Funds Receivable or Payable for the Benefit of Members [Table] Number of members Number Of Members Represents the number of members under the government-sponsored health care programs. Number of states the entity serves Number of States in which Entity Operates Premiums receivable, net Premiums Receivable, Net Premiums payable, net Unearned Premiums Medicaid retroactive rate change and risk score adjustments Medicaid Retroactive Rate Change and Risk Score Adjustments Medicaid Retroactive Rate Change and Risk Score Adjustments Funds payable for the benefit of members Funds Payable For The Benefit of Members Funds held (payable) or receivable for the benefit of members represent government payments received or to be received to subsidize the member portion of medical payments for certain of our stand-alone prescription drug program members. We do not bear underwriting risk since such funds represent pass-through payments from our government partners to fund deductibles, co-payments and other participant benefits. ACA industry fee liability ACA Industry Fee ACA Industry Fee Liability ACA industry fee expense ACA Industry Fee Expense ACA Industry Fee Expense Medicaid ACA industry fee reimbursement revenue Medicaid ACA Industry Fee Reimbursement Revenue Medicaid ACA Industry Fee Reimbursement Revenue Earnings Per Share [Abstract] EARNINGS PER COMMON SHARE Earnings Per Share [Text Block] Commitments and Contingencies Disclosure [Abstract] Loss Contingencies [Table] Loss Contingencies [Table] Loss Contingency Nature [Axis] Loss Contingency Nature [Axis] Loss Contingency, Nature [Domain] Loss Contingency, Nature [Domain] Derivative Lawsuits Derivative Lawsuits [Member] A lawsuit brought by a corporation shareholder against the directors, management and/or other shareholders of the corporation, for a failure by management. Litigation Case [Axis] Litigation Case [Axis] Litigation Case [Domain] Litigation Case [Domain] Mr. Farha Case Mr. Farha Case [Member] Mr. Farha Case [Member] Mr. Behrens Case Mr. Behrens Case [Member] Mr. Behrens Case [Member] Mr. Bereday Case Mr. Bereday Case [Member] Mr. Bereday Case Legal Entity [Axis] Legal Entity [Axis] Entity [Domain] Entity [Domain] Securities and Exchange Commission (SEC) United States Securities And Exchange Commission [Member] United States Securities And Exchange Commission [Member] Loss Contingencies [Line Items] Loss Contingencies [Line Items] Number of former officers receiving notices of cross appeal Number Of Former Employees Receiving Notices of Cross Appeal Number Of Former Employees Receiving Notices of Cross Appeal Number of former associates being pursued in action filed by entity Number Of Former Associates Being Pursued In Action Filed By Entity Number Of Former Associates Being Pursued In Action Filed By Entity Number of former employees found guilty and appealing Number Of Former Employees Found Guilty and Appealing Number Of Former Employees Found Guilty and Appealing Number of former employees being pursued in action filed by entity Number Of Former Employees Being Pursued In Action Filed By Entity Number Of Former Employees Being Pursued In Action Filed By Entity Number of actions filed in the federal and state courts between October 2007 and January 2008 Number of actions filed in the Federal Court The number of actions filed in Federal Court related to government investigations in a derivative action filed against the entity. Number of former executives being pursued in action filed by entity Number Of Former Officers Being Pursued In Action Filed By Entity The number of former officers being pursued in an action filed by the entity pursuant to a report filed by the Special Litigation Committee to the Federal Court determining, among other things, that the entity should pursue such an action. Settlement agreement, amount awarded Litigation Settlement, Amount Awarded from Other Party Maximum legal fee obligation Litigation Settlement, Legal Fee Advances, Maximum Litigation Settlement, Legal Fee Advances, Maximum Legal fees Legal Fees Business Combinations [Abstract] Fair Value of Consideration Transferred in Acquisition Schedule of Business Acquisitions, by Acquisition [Table Text Block] Fair Values of Assets Acquired and Liabilities Assumed Schedule of Recognized Identified Assets Acquired and Liabilities Assumed [Table Text Block] Final Fair Values and Weighted Average Useful Lives for Identifiable Intangible Assets Acquired Schedule of Finite-Lived Intangible Assets Acquired as Part of Business Combination [Table Text Block] Unaudited Pro Forma Results Business Acquisition, Pro Forma Information [Table Text Block] Investments, Debt and Equity Securities [Abstract] Short-term and Long-term Investments by Security Type Debt Securities, Available-for-sale [Table Text Block] Contractual Maturities of Available-for-sale Securities Investments Classified by Contractual Maturity Date [Table Text Block] MEDICAL BENEFITS PAYABLE [Abstract] Liability for Claims and Claims Adjustment Expense [Table] Liability for Claims and Claims Adjustment Expense [Table] Segments [Domain] Medicare Health Plans Medicare Health Plans [Member] Medicare Health Plans Segment [Member] Medicare PDPs Prescription Drug Plans [Member] A reportable segment within the Medicare business line through which the entity offers Medicare Part D coverage to Medicare-eligible beneficiaries. Liability for Claims and Claims Adjustment Expense [Line Items] Liability for Claims and Claims Adjustment Expense [Line Items] Reconciliation of the beginning and ending balance of medical benefits payable [Roll Forward] Reconciliation of the beginning and ending balance of medical benefits payable [Roll Forward] A roll forward is a reconciliation of the beginning and ending balance of medical benefits payable. Beginning balance (1) Liability for Claims and Claims Adjustment Expense Acquisitions Liability for Unpaid Claims and Claims Adjustment Expense, Business Acquisitions Medical benefits incurred related to Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract] Current year Current Year Claims and Claims Adjustment Expense Prior years Prior Year Claims and Claims Adjustment Expense Total Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims Medical benefits paid related to Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract] Current year Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Current Year Prior years Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Prior Years Total Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid Ending balance (1) Premium deficiency reserve Deferred Tax Assets, Premium Deficiency Reserve Deferred Tax Assets, Premium Deficiency Reserve Discontinued Operations and Disposal Groups [Abstract] DISCONTINUED OPERATIONS Disposal Groups, Including Discontinued Operations, Disclosure [Text Block] Disposal Groups, Including Discontinued Operations [Table] Disposal Groups, Including Discontinued Operations [Table] Disposal Group Name [Axis] Disposal Group Name [Axis] Disposal Group Name [Domain] Disposal Group Name [Domain] Traditional Insurance Business Traditional Insurance Business [Member] Traditional Insurance Business [Member] Disposal Group Classification [Axis] Disposal Group Classification [Axis] Disposal Group Classification [Domain] Disposal Group Classification [Domain] Discontinued operations, held-for-sale Discontinued Operations, Held-for-sale [Member] Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] Assets Assets [Abstract] Cash and cash equivalents Disposal Group, Including Discontinued Operation, Cash and Cash Equivalents Investments Disposal Group, Including Discontinued Operation, Investments Disposal Group, Including Discontinued Operation, Investments Reinsurance recoverables Disposal Group, Including Discontinued Operation, Reinsurance Recoverables Disposal Group, Including Discontinued Operation, Reinsurance Recoverables Other assets Disposal Group, Including Discontinued Operation, Other Assets Total Assets Disposal Group, Including Discontinued Operation, Assets Liabilities Liabilities [Abstract] Reserves and other policy liabilities Disposal Group, Including Discontinued Operation, Accrued Liabilities Other liabilities Disposal Group, Including Discontinued Operation, Other Liabilities Total liabilities Disposal Group, Including Discontinued Operation, Liabilities, Noncurrent Income Tax Disclosure [Abstract] INCOME TAXES Income Tax Disclosure [Text Block] Weighted-average common shares outstanding — basic (in shares) Weighted Average Number of Shares Outstanding, Basic Dilutive effect of outstanding stock-based compensation awards (in shares) Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements Weighted-average common shares outstanding — diluted (in shares) Weighted Average Number of Shares Outstanding, Diluted Anti-dilutive stock-based compensation awards excluded from computation (in shares) Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Total Assets and Liabilities of Discontinued Operations Disposal Groups, Including Discontinued Operations [Table Text Block] Proceeds from sale of available-for-sale investments Proceeds from Sale of Debt Securities, Available-for-sale Debt Securities, Available-for-sale, Realized Loss Debt Securities, Available-for-sale, Realized Loss Realized gains and losses on sales and redemptions of investments Debt Securities, Available-for-sale, Realized Gain (Loss) Other than temporary impairment losses Other-than-temporary Impairment Loss, Debt Securities, Available-for-sale Available-for-sale securities, gross realized gains Debt Securities, Available-for-sale, Realized Gain Debt Disclosure [Abstract] DEBT Debt Disclosure [Text Block] Statement of Financial Position [Abstract] Assets Current Assets: Assets, Current [Abstract] Cash and cash equivalents Cash and Cash Equivalents, at Carrying Value Short-term investments Short-term Investments Pharmacy rebates receivable, net Other Receivables, Net, Current Receivables from government partners Receivables from government partners Receivables from government partners Funds receivable for the benefit of members Funds Receivable For The Benefit Of Members Funds held or receivable for the benefit of members represent government payments received or to be received to subsidize the member portion of medical payments for certain of our stand-alone prescription drug program members. We do not bear underwriting risk since such funds represent pass-through payments from our government partners to fund deductibles, co-payments and other participant benefits. Deferred ACA industry fee Deferred ACA Industry Fee Asset Deferred ACA Industry Fee Asset Prepaid expenses and other current assets, net Prepaid Expense and Other Assets, Current Total current assets Assets, Current Property, equipment and capitalized software, net Property, Plant and Equipment, Net Goodwill Goodwill Other intangible assets, net Intangible Assets, Net (Excluding Goodwill) Long-term investments Long-term Investments Restricted cash, cash equivalents and investments Restricted Cash and Cash Equivalents, Noncurrent Other assets Other Assets, Noncurrent Assets of discontinued operations Disposal Group, Including Discontinued Operation, Assets, Noncurrent Total Assets Assets Liabilities and Stockholders' Equity Liabilities and Equity [Abstract] Current Liabilities: Liabilities, Current [Abstract] Medical benefits payable Unearned premiums Accounts payable and accrued expenses Accounts Payable and Other Accrued Liabilities, Current Other payables to government partners Other Payables To Government Partners Other payables due to government partners represent amounts due to government agencies under various contractual and plan arrangements. We estimate the amounts due to CMS for risk protection under the risk corridor provisions of our contract with CMS each period based on pharmacy claims experience. Also this line item includes reserves for the return of premium on minimum loss ratio guarantees for certain state Medicaid contracts. Total current liabilities Liabilities, Current Deferred income tax liability, net Deferred Income Tax Liabilities, Net Long-term debt, net Long-term Debt, Excluding Current Maturities Other liabilities Other Liabilities, Noncurrent Liabilities of discontinued operations Total Liabilities Liabilities Commitments and contingencies Commitments and Contingencies Stockholders' Equity: Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest [Abstract] Preferred stock, $0.01 par value (20,000,000 authorized, no shares issued or outstanding) Preferred Stock, Value, Issued Common stock, $0.01 par value (100,000,000 authorized, 44,767,277 and 44,522,988 shares issued and outstanding at June 30, 2018 and December 31, 2017, respectively) Common Stock, Value, Issued Paid-in capital Additional Paid in Capital Retained earnings Retained Earnings (Accumulated Deficit) Accumulated other comprehensive loss Accumulated Other Comprehensive Income (Loss), Net of Tax Total Stockholders' Equity Stockholders' Equity Attributable to Parent Total Liabilities and Stockholders' Equity Liabilities and Equity Debt Securities, Available-for-sale [Table] Debt Securities, Available-for-sale [Table] Financial Instrument [Axis] Financial Instrument [Axis] Financial Instruments [Domain] Financial Instruments [Domain] Asset-backed securities Asset-backed Securities [Member] Corporate debt securities Corporate Debt Securities [Member] Municipal securities Municipal Bonds [Member] Residential mortgage-backed securities Residential Mortgage Backed Securities [Member] Short-term time deposits Bank Time Deposits [Member] Government and agency obligations US Government Agencies Debt Securities [Member] Other securities Other Security Investments [Member] Debt Securities, Available-for-sale [Line Items] Debt Securities, Available-for-sale [Line Items] Amortized Cost Debt Securities, Available-for-sale, Amortized Cost Gross Unrealized Gains Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax Gross Unrealized Losses Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax Estimated Fair Value Debt Securities, Available-for-sale Restricted Investments Note [Abstract] RESTRICTED CASH, CASH EQUIVALENTS AND INVESTMENTS Restricted Assets Disclosure [Text Block] Reconciliation of the Beginning and Ending Balances of Medical Benefits Payable, by Segment Reconciliation of Medical Benefits Payable [Table Text Block] A reconciliation of the beginning and ending balances of medical benefits payable, including separate disclosure of medical benefits incurred and medical benefits paid during the reporting period. Fair Value Disclosures [Abstract] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table] Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Domain] Fair Value Hierarchy and NAV [Domain] Significant Unobservable Inputs (Level 3) Fair Value, Inputs, Level 3 [Member] Measurement Frequency [Axis] Measurement Frequency [Axis] Fair Value, Measurement Frequency [Domain] Fair Value, Measurement Frequency [Domain] Fair value, measurements, recurring Fair Value, Measurements, Recurring [Member] Asset backed securities Auction Rate Securities [Member] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] Beginning balance Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value Realized gains (losses) in earnings Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings Changes in unrealized gains (losses) in other comprehensive income Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Other Comprehensive Income (Loss) Purchases, sales and redemptions Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases, (Sales), Issuances, (Settlements) Net transfers in or (out) of Level 3 Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers, Net Ending balance Subsequent Events [Abstract] SUBSEQUENT EVENTS Subsequent Events [Text Block] FAIR VALUE MEASUREMENTS Fair Value Disclosures [Text Block] Statement of Stockholders' Equity [Abstract] Statement [Table] Statement [Table] Statement, Equity Components [Axis] Equity Components [Axis] Equity Component [Domain] Equity Component [Domain] Common Stock Common Stock [Member] Paid in Capital Additional Paid-in Capital [Member] Retained Earnings Retained Earnings [Member] Accumulated Other Comprehensive Income (Loss) AOCI Attributable to Parent [Member] Statement [Line Items] Statement [Line Items] Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Beginning balance (in shares) Common Stock, Shares, Outstanding Beginning balance Common stock issued for vested stock-based compensation awards (in shares) Stock Issued During Period, Shares, Share-based Compensation, Net of Forfeitures Repurchase and retirement of shares to satisfy tax withholding requirements (in shares) Stock Repurchased During Period, Shares Repurchase and retirement of shares to satisfy tax withholding requirements Stock Repurchased During Period, Value Stock-based compensation expense, net of forfeitures Adjustments to Additional Paid in Capital, Share-based Compensation, Requisite Service Period Recognition Comprehensive income Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest Ending balance (in shares) Ending balance ORGANIZATION, BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES Organization, Consolidation and Presentation of Financial Statements Disclosure and Significant Accounting Policies [Text Block] Restrictions on Cash and Cash Equivalents [Table] Restrictions on Cash and Cash Equivalents [Table] Restricted Cash and Cash Equivalents, Cash and Cash Equivalents [Axis] Restricted Cash and Cash Equivalents [Axis] Restricted Cash and Cash Equivalents, Cash and Cash Equivalents [Domain] Cash and Cash Equivalents [Domain] Cash Cash [Member] Money market funds Money Market Funds [Member] U.S. government securities and other US Treasury and Government [Member] Restricted Cash and Cash Equivalents Items [Line Items] Restricted Cash and Cash Equivalents Items [Line Items] Amortized Cost Restricted Investments, Amortized Cost Basis Restricted Investments, Amortized Cost Basis Gross Unrealized Gains Restricted Investments, Gross Unrealized Gain, Before Tax Restricted Investments, Gross Unrealized Gain, Before Tax Gross Unrealized Losses Restricted Investments, Gross Unrealized Losses, Before Tax Restricted Investments, Gross Unrealized Losses, Before Tax Estimated Fair Value Schedule of Outstanding Debt Obligations Schedule of Long-term Debt Instruments [Table Text Block] MEDICAL BENEFITS PAYABLE Medical Benefits Payable [Text Block] Description and amounts of medical benefits payable at the end of the reporting period and other information and schedules needed to disclose the medical benefit payable account. Segment Reporting [Abstract] Schedule of Revenues from External Customers and Long-Lived Assets [Table] Schedule of Revenues from External Customers and Long-Lived Assets [Table] Geographical [Axis] Geographical [Axis] Geographical [Domain] Geographical [Domain] Kentucky KENTUCKY Florida FLORIDA Georgia GEORGIA Revenues from External Customers and Long-Lived Assets [Line Items] Revenues from External Customers and Long-Lived Assets [Line Items] Premium revenue as a percentage of total consolidated premium revenue Premium Revenue, Net Of Premium Tax Represents premium revenue net of premium tax of consolidated premium revenue. Disclosure of Compensation Related Costs, Share-based Payments [Abstract] Summary of Stock Unit Award Activity Schedule of Share-based Compensation, Restricted Stock and Restricted Stock Units Activity [Table Text Block] Schedule of Business Acquisitions, by Acquisition [Table] Schedule of Business Acquisitions, by Acquisition [Table] Universal American Universal American [Member] Universal American [Member] Business Acquisition [Axis] Business Acquisition [Axis] Business Acquisition, Acquiree [Domain] Business Acquisition, Acquiree [Domain] Class of Stock [Axis] Class of Stock [Axis] Class of Stock [Domain] Class of Stock [Domain] Preferred Stock Preferred Stock [Member] Award Type [Axis] Award Type [Axis] Equity Award [Domain] Equity Award [Domain] Stock-based Award Stock Compensation Plan [Member] Long-term Debt, Type [Axis] Long-term Debt, Type [Axis] Long-term Debt, Type [Domain] Long-term Debt, Type [Domain] Senior Notes Senior Notes [Member] Debt Instrument [Axis] Debt Instrument [Axis] Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] 4.00% Convertible Senior Notes 4.00% Convertible Senior Notes [Member] 4.00% Convertible Senior Notes [Member] Business Acquisition [Line Items] Business Acquisition [Line Items] Business Combination, Consideration Transferred [Abstract] Business Combination, Consideration Transferred [Abstract] Cash consideration transferred Payments to Acquire Businesses, Gross Assumed debt Business Combination, Consideration Transferred, Liabilities Incurred Equity interests issued Business Combination, Consideration Transferred, Equity Interests Issued and Issuable Total consideration transferred Business Combination, Consideration Transferred Common stock, outstanding (in shares) Interest rate Debt Instrument, Interest Rate, Stated Percentage Payments for repurchase of preferred shares Payments for Repurchase of Redeemable Preferred Stock Payments for repurchase of preferred shares and accrued dividends Payments for Repurchase of Redeemable Preferred Stock, Including Ordinary Dividends Payments for Repurchase of Redeemable Preferred Stock, Including Ordinary Dividends Payments of accrued dividends Payments of Ordinary Dividends, Preferred Stock and Preference Stock Unrecognized stock based compensation cost Acquisition Related Compensation Cost Acquisition Related Compensation Cost Preferred stock, par value (in USD per share) Preferred Stock, Par or Stated Value Per Share Preferred stock, authorized (in shares) Preferred Stock, Shares Authorized Preferred stock, issued (in shares) Preferred Stock, Shares Issued Preferred stock, outstanding (in shares) Preferred Stock, Shares Outstanding Common stock, par value (in USD per share) Common Stock, Par or Stated Value Per Share Common stock, authorized (in shares) Common Stock, Shares Authorized Common stock, issued (in shares) Common Stock, Shares, Issued Reconciliation of Cash, Cash Equivalents and Restricted Cash Restrictions on Cash and Cash Equivalents [Table Text Block] Reconciliation of Cash, Cash Equivalents and Restricted Cash Schedule of Cash and Cash Equivalents [Table Text Block] Finite-Lived Intangible Assets Acquired as Part of Business Combination [Table] Finite-Lived Intangible Assets Acquired as Part of Business Combination [Table] Finite-Lived Intangible Assets by Major Class [Axis] Finite-Lived Intangible Assets by Major Class [Axis] Finite-Lived Intangible Assets, Major Class Name [Domain] Finite-Lived Intangible Assets, Major Class Name [Domain] Membership Customer-Related Intangible Assets [Member] Tradenames Trade Names [Member] Provider network Provider Network [Member] Provider networks are lists of physicians and hospitals that provide services to a health insurance plan. Other Other Intangible Assets [Member] Acquired Finite-Lived Intangible Assets [Line Items] Acquired Finite-Lived Intangible Assets [Line Items] Gross fair value Finite-lived Intangible Assets Acquired Weighted average useful life Acquired Finite-lived Intangible Assets, Weighted Average Useful Life INVESTMENTS Investments in Debt and Marketable Equity Securities (and Certain Trading Assets) Disclosure [Text Block] Schedule of Segment Reporting Information, by Segment [Table] Schedule of Segment Reporting Information, by Segment [Table] Name of Healthcare Plan [Axis] Name of Healthcare Plan [Axis] Name of Healthcare Plan [Axis] Name of Healthcare Plan [Domain] Name of Healthcare Plan [Domain] [Domain] for Name of Healthcare Plan [Axis] Medical Services Managed Care Plan Medical Services Managed Care Plan [Member] Medical Services Managed Care Plan [Member] Serious Mental Illness Specialty Plan Serious Mental Illness Specialty Plan [Member] Serious Mental Illness Specialty Plan [Member] Subsequent Event Type [Axis] Subsequent Event Type [Axis] Subsequent Event Type [Domain] Subsequent Event Type [Domain] Subsequent Event Subsequent Event [Member] Segment Reporting Information [Line Items] Segment Reporting Information [Line Items] Number of reportable segments Number of Reportable Segments Number of beneficiaries Number of Beneficiaries Number of Beneficiaries Term of agreement Term of Agreement Term of Agreement Calculation of the Weighted-Average Common Shares Outstanding - Diluted Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Debt securities Debt Securities [Member] Within 1 Year Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, within One Year, Fair Value 1 Through 5 Years Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, after One Through Five Years, Fair Value 5 Through 10 Years Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, after Five Through Ten Years, Fair Value Thereafter Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, after 10 Years, Fair Value Document and Entity Information [Abstract] Document and Entity Information [Abstract] Entity Registrant Name Entity Registrant Name Entity Central Index Key Entity Central Index Key Current Fiscal Year End Date Current Fiscal Year End Date Entity Filer Category Entity Filer Category Entity Common Stock, Shares Outstanding (in shares) Entity Common Stock, Shares Outstanding Document Fiscal Year Focus Document Fiscal Year Focus Document Fiscal Period Focus Document Fiscal Period Focus Document Type Document Type Amendment Flag Amendment Flag Document Period End Date Document Period End Date Revenue by Geographic Location Schedule of Revenue from External Customers and Long-Lived Assets, by Geographical Areas [Table Text Block] Segment Results Schedule of Segment Reporting Information, by Segment [Table Text Block] SEGMENT REPORTING Segment Reporting Disclosure [Text Block] Realized gains (losses) on restricted investments Restricted Investments, Realized Gains (Losses) Restricted Investments, Realized Gains (Losses) Schedule of Long-term Debt Instruments [Table] Schedule of Long-term Debt Instruments [Table] Measurement Basis [Axis] Measurement Basis [Axis] Fair Value Measurement [Domain] Fair Value Measurement [Domain] Portion at Fair Value Measurement Portion at Fair Value Measurement [Member] Carrying Value Reported Value Measurement [Member] Fair Value Hierarchy and NAV [Domain] Quoted Prices in Active Markets for Identical Assets (Level 1) Fair Value, Inputs, Level 1 [Member] Significant Other Observable Inputs (Level 2) Fair Value, Inputs, Level 2 [Member] Credit Facility [Axis] Credit Facility [Axis] Credit Facility [Domain] Credit Facility [Domain] Revolving Credit Facility Revolving Credit Facility [Member] Debt Instrument [Line Items] Debt Instrument [Line Items] Long-term debt, fair value Long-term Debt, Fair Value Borrowings outstanding Long-term Line of Credit, Noncurrent Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] RSUs Restricted Stock Units (RSUs) [Member] PSUs Performance Shares [Member] MSUs Market Stock Units [Member] Market stock units (MSUs) as awarded by a company to their employees as a form of incentive compensation. Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Equity Instruments Other than Options [Roll Forward] Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] Outstanding as of beginning of period (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number Granted (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period Vested (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period Forfeited (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period Outstanding at end of period (in shares) Cash and cash equivalents Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents Investments, including restricted investments Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Investments Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Investments Premiums receivable, net Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Premiums Receivable Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Premiums Receivable Pharmacy rebates receivable, net, and other current assets Business Combination, Recognized Identifiable Assets Acquired And Liabilities Assumed, Pharmacy Rebates Receivable And Other Current Assets Business Combination, Recognized Identifiable Assets Acquired And Liabilities Assumed, Pharmacy Rebates Receivable and Other Current Assets Property, equipment and capitalized software, net Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment Other intangible assets, net Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill Assets of discontinued operations Business Combinations, Recognized Identifiable Assets Acquired And Liabilities Consumed, Assets From Discontinued Operations Business Combinations, Recognized Identifiable Assets Acquired And Liabilities Consumed, Assets From Discontinued Operations Fair value of total assets acquired Business Combination, Recognized Identifiable Assets Acquired And Liabilities Assumed, Assets Acquired Including Goodwill Business Combination, Recognized Identifiable Assets Acquired And Liabilities Assumed, Assets Acquired Including Goodwill Medical benefits payable Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Medical Benefits Payable Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Medical Benefits Payable Deferred tax liabilities, net Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Liabilities Other liabilities Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Other Liabilities Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Other Liabilities Liabilities of discontinued operations Business Combinations, Recognized Identifiable Assets Acquired And Liabilities Consumed, Liabilities Of Discontinued Operations Business Combinations, Recognized Identifiable Assets Acquired And Liabilities Consumed, Discontinued Operations From Liabilities Fair value of liabilities assumed Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities Fair value of net assets acquired Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net Effective income tax rate Effective Income Tax Rate Reconciliation, Percent Discrete tax benefit Income Tax Expense (Benefit), Discrete Items Income Tax Expense (Benefit), Discrete Items Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Table] Fair Value Measurements, Recurring and Nonrecurring [Table] Fair Value by Measurement Frequency [Axis] Schedule of Available-for-sale Securities, Major Types of Debt and Equity Securities [Axis] Government and agency obligations U.S. government securities and other US Treasury Securities [Member] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Investments Investments, Fair Value Disclosure Restricted cash, cash equivalents and investments Restricted Investment, Fair Value Disclosure This element represents restricted investments reported on the balance sheet at period end measured at fair value by the entity. This element in intended to be used in connection with fair value disclosures required in the footnote disclosures to the financial statements. Favorable development of medical benefits payable Favorable development of medical benefits payable excluding the release of the provision for moderately adverse conditions Net Favorable (Unfavorable) Development of Medical Benefits Payable, Excluding Release of the Provision for Moderately Adverse Conditions Net Favorable (Unfavorable) Development of Medical Benefits Payable, Excluding Release of the Provision for Moderately Adverse Conditions 5.25% Senior Notes, due April 1, 2025 5.25 Percent Senior Notes Due 2025, Issued 2017 [Member] 5.25 Percent Senior Notes Due 2025, Issued 2017 [Member] 5.75% Senior Notes, due November 15, 2020 5.75 Percent Senior Notes Due 2020, Issued 2015 [Member] 5.75 Percent Senior Notes Due 2020, Issued 2015 [Member] Aggregate principal amount Debt Instrument, Face Amount Issue price percentage Debt Instrument, Issue Price, Percentage Debt Instrument, Issue Price, Percentage Aggregate net proceeds from the issuance of debt Proceeds from Issuance of Debt Debt repurchase amount Debt Instrument, Repurchase Amount Redemption price Debt Instrument, Redemption Price, Percentage Credit facility, maximum borrowing capacity Line of Credit Facility, Maximum Borrowing Capacity Repayments of debt Repayments of Debt Schedule of Restricted Investments Schedule of Restricted Investments [Table Text Block] [Table Text Block] for Schedule of Restricted Investments [Table] PHP and Universal American PHP and Universal American [Member] PHP and Universal American [Member] Business Acquisition, Pro Forma Information [Abstract] Business Acquisition, Pro Forma Information [Abstract] Total revenues Business Acquisition, Pro Forma Revenue Net income Business Acquisition, Pro Forma Net Income (Loss) Earnings per common share: Basic (in USD per share) Business Acquisition, Pro Forma Earnings Per Share, Basic Diluted (in USD per share) Business Acquisition, Pro Forma Earnings Per Share, Diluted STOCK-BASED COMPENSATION Disclosure of Compensation Related Costs, Share-based Payments [Text Block] Restricted cash and cash equivalents Restricted Cash and Cash Equivalents Total cash, cash equivalents, and restricted cash and cash equivalents Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents Statement of Cash Flows [Abstract] Cash flows from operating activities: Net Cash Provided by (Used in) Operating Activities [Abstract] Net income Net Income (Loss) Attributable to Parent Adjustments to reconcile net income to cash flows from operating activities: Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Depreciation and amortization Depreciation, Depletion and Amortization, Nonproduction Loss on extinguishment of debt Gain (Loss) on Extinguishment of Debt Stock-based compensation expense Share-based Compensation Deferred taxes, net Deferred Income Tax Expense (Benefit) Other, net Other Operating Activities, Cash Flow Statement Changes in operating accounts, net of effects from acquisitions: Increase (Decrease) in Operating Capital [Abstract] Premiums receivable, net Increase (Decrease) in Premiums Receivable Pharmacy rebates receivable, net Increase (Decrease) in Other Receivables Medical benefits payable Increase (Decrease) in Health Care Insurance Liabilities Unearned premiums Increase (Decrease) in Unearned Premiums Other payables to government partners Increase Decrease In Other Payables To Government Partners The net change during the reporting period in amounts due to government agencies under various contractual and plan arrangements. We estimate the amounts due from CMS for risk protection under the risk corridor provisions of our contract with CMS each period based on pharmacy claims experience. Accrued liabilities and other, net Increase (Decrease) in Accrued Liabilities and Other Operating Liabilities Net cash provided by operating activities Net Cash Provided by (Used in) Operating Activities Cash flows from investing activities: Net Cash Provided by (Used in) Investing Activities [Abstract] Acquisitions and acquisition-related settlements, net of cash acquired Payments to Acquire Businesses, Net of Cash Acquired Purchases of investments Payments to Acquire Investments Proceeds from sales and maturities of investments Proceeds from Sale, Maturity and Collection of Investments Additions to property, equipment and capitalized software, net Payments to Acquire Productive Assets Net cash used in investing activities Net Cash Provided by (Used in) Investing Activities Cash flows from financing activities: Net Cash Provided by (Used in) Financing Activities [Abstract] Proceeds from issuance of debt, net of financing costs paid Proceeds from Issuance of Long-term Debt Payments on debt Repayments of Short-term Debt Repurchase and retirement of shares to satisfy employee tax withholding requirements Payments Related to Tax Withholding for Share-based Compensation Funds received for the benefit of members, net Proceeds from (Payments for) the Benefit of Members Proceeds from (Payments for) the Benefit of Members Other, net Proceeds from (Payments for) Other Financing Activities Net cash provided by financing activities Net Cash Provided by (Used in) Financing Activities Increase (decrease) in cash, cash equivalents and restricted cash and cash equivalents Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect Balance at beginning of period Balance at end of period SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION: Supplemental Cash Flow Information [Abstract] Cash paid for taxes, net of refunds Income Taxes Paid, Net Cash paid for interest Interest Paid, Excluding Capitalized Interest, Operating Activities SUPPLEMENTAL DISCLOSURES OF NON-CASH TRANSACTIONS: Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract] Non-cash additions to property, equipment, and capitalized software Capital Expenditures Incurred but Not yet Paid Basis of Presentation Basis of Accounting, Policy [Policy Text Block] Use of Estimates Use of Estimates, Policy [Policy Text Block] Reclassifications Reclassification, Policy [Policy Text Block] Premium Receivable and Unearned Premiums Revenue from Contract with Customer [Policy Text Block] Medicare Part D Settlements Funds Receivable/Payable for the Benefit of Members [Policy Text Block] [Table Text Block] for Disclosure of accounting policy for Funds Receivable or Payable for the Benefit of Members [Table] ACA Industry Fee ACA Industry Fee [Policy Text Block] ACA Industry Fee [Policy Text Block] Accounting Standards Recently Adopted and Pending Adoption New Accounting Pronouncements, Policy [Policy Text Block] Income Statement [Abstract] Revenues: Revenues [Abstract] Premium Premiums Earned, Net Investment and other income Investment And Other Income Investment income represents income derived from bank deposits and investments in securities consisting of interest income from cash instruments and securities, dividend income, and income or expense derived from the amortization of investment related discounts or premiums, respectively. Total revenues Revenues Expenses: Cost of Revenue [Abstract] Medical benefits Policyholder Benefits and Claims Incurred, Net, Health Selling, general and administrative Selling, General and Administrative Expense ACA industry fee Medicaid premium taxes Premium Tax Expense An assessment levied by a state government agency on premium revenue. Depreciation and amortization Interest Interest Expense Total expenses Operating Expenses Income from operations Operating Income (Loss) Income before income taxes and equity in losses of unconsolidated subsidiaries Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest Equity in losses of unconsolidated subsidiaries Income (Loss) from Equity Method Investments Income before income taxes Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Income tax expense Income Tax Expense (Benefit) Net income Other comprehensive income (loss), before tax: Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract] Change in net unrealized gains and losses on available-for-sale securities Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, before Tax Income tax expense (benefit) related to other comprehensive income Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, Tax Other comprehensive income (loss), net of tax Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent Comprehensive income Comprehensive Income (Loss), Net of Tax, Attributable to Parent Basic (in USD per share) Earnings Per Share, Basic Diluted (in USD per share) Earnings Per Share, Diluted Weighted average common shares outstanding: Earnings Per Share, Basic and Diluted, Other Disclosures [Abstract] Basic (in shares) Diluted (in shares) Assets and Liabilities Measured at Fair Value on a Recurring Basis Fair Value, by Balance Sheet Grouping [Table Text Block] Carrying Value and Fair Value of Long-term Debt Schedule of Carrying Values and Estimated Fair Values of Debt Instruments [Table Text Block] Changes in the Fair Value of Auction Rate Securities Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block] Subsequent Event [Table] Subsequent Event [Table] Revolving Credit Agreement Due July 2023 Revolving Credit Agreement Due July 2023 [Member] Revolving Credit Agreement Due July 2023 [Member] Range [Axis] Range [Axis] Range [Domain] Range [Domain] Minimum Minimum [Member] Maximum Maximum [Member] ABR Loans ABR Loans [Member] ABR Loans [Member] Eurodollar Eurodollar [Member] Variable Rate [Axis] Variable Rate [Axis] Variable Rate [Domain] Variable Rate [Domain] London Interbank Offered Rate (LIBOR) London Interbank Offered Rate (LIBOR) [Member] Subsequent Event [Line Items] Subsequent Event [Line Items] Debt instrument, basis spread on variable rate Debt Instrument, Basis Spread on Variable Rate Accordion feature amount Line of Credit Facility, Maximum Borrowing Capacity, Accordion Feature Increase Line of Credit Facility, Maximum Borrowing Capacity, Accordion Feature Increase Unused commitment fee percentage Line of Credit Facility, Commitment Fee Percentage ACQUISITIONS Business Combination Disclosure [Text Block] Long-term debt, net Long-term Debt, Excluding Current Maturities [Abstract] Senior notes Senior Notes, Noncurrent Revolving Credit Facility Debt issuance costs Debt Issuance Costs, Noncurrent, Net Total long-term debt, net Consolidation Items [Axis] Consolidation Items [Axis] Consolidation Items [Domain] Consolidation Items [Domain] Operating Segments Operating Segments [Member] Segment Reconciling Items Segment Reconciling Items [Member] Premium revenue Medical benefits expense Gross margin Gross Profit Investment and other income Other expenses Other Expenses COMMITMENTS AND CONTINGENCIES Commitments and Contingencies Disclosure [Text Block] Meridian Meridian [Member] Meridian [Member] Phoenix Health Plan Phoenix Health Plan [Member] Phoenix Health Plan [Member] Senior Unsecured Notes Unsecured Debt [Member] 5.75 Percent Senior Notes Due 2020, Issued 2015 [Member] Convertible Senior Notes Due 2021 Convertible Senior Notes Due 2021 [Member] Convertible Senior Notes Due 2021 [Member] Acquisition consideration transferred Business Acquisition, Equity Interest Issued or Issuable, Value Assigned Business Acquisition, Equity Interest Issued or Issuable, Value Assigned Committed bridge financing Bridge Loan Number of members acquired Number of Members Acquired Number of Members Acquired Cash purchase price (in USD per share) Business Acquisition, Share Price Assumption of convertible debt Net deferred tax liabilities acquired Expected tax deductible amount of goodwill and other intangible assets acquired Business Acquisition, Goodwill, Expected Tax Deductible Amount Proceeds from convertible notes Proceeds from Convertible Debt Preferred shares issued Temporary Equity, Stock Issued During Period, Value, New Issues Preferred stock issued (in shares) Temporary Equity, Shares Issued Liquidation preference (in USD per share) Preferred Stock, Liquidation Preference Per Share Preferred shares redeemed Preferred Stock, Redemption Amount Preferred shares par value Temporary Equity, Par Value Preferred shares accrued dividends Dividends, Preferred Stock Consideration transferred, preferred shares redemption amount Revenue Pre-tax income Transaction and integration-related costs incurred Business Combination, Separately Recognized Transactions, Additional Disclosures, Acquisition Cost Expensed Award Type [Domain] Performance Stock Units Compensation expense Unrecognized compensation cost Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized Weighted-average period over which compensation costs are expected to be recognized Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition Closing common stock price (in USD per share) Share Price Grants in period, weighted average grant date fair value (in USD per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value