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Cash Provided by (Used in) Operating Activity, Other Item Shares outstanding at the beginning of the period (in shares) Shares, Outstanding, Excluding Restricted Stock Awards Shares, Outstanding, Excluding Restricted Stock Awards Dividends or Other Earnings Paid on Equity Awards not Otherwise Reflected in Total Compensation for Covered Year Dividends or Other Earnings Paid on Equity Awards not Otherwise Reflected in Total Compensation for Covered Year [Member] Income Taxes Income Tax, Policy [Policy Text Block] Net cash provided by (used in) operating activities Cash Provided by (Used in) Operating Activity, Including Discontinued Operation Prior years Prior period claims, favorable development Prior Year Claims and Claims Adjustment Expense Stockholders’ equity: Equity, Attributable to Parent [Abstract] Income Statement [Abstract] Income Statement [Abstract] Document Transition Report Document Transition Report Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] 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Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment and Tax Due in one year or less Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, Year One Retained Earnings Retained Earnings [Member] Credit Facility Revolving Credit Facility [Member] Erroneously Awarded Compensation Recovery Erroneously Awarded Compensation Recovery [Table] Number of states with programs Number Of States With Government-Sponsored Healthcare Programs Number Of States With Government-Sponsored Healthcare Programs Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Common stock, shares outstanding (in shares) Beginning balance (in shares) Ending balance (in shares) Common Stock, Shares, Outstanding Award Timing Disclosures [Line Items] Corporate debt securities Corporate Debt Securities [Member] Net income per share - diluted (in dollars per share) Earnings Per Share, Diluted Entity Current Reporting Status Entity Current Reporting Status Net cash used in financing activities Cash Provided by (Used in) Financing Activity, Including Discontinued Operation Total Shareholder Return Amount Total Shareholder Return Amount 6.500% Notes due February 15, 2031 6.500% Senior Notes Due 2031 [Member] 6.500% Senior Notes Due 2031 Prepaid expenses and other current assets Increase (Decrease) in Prepaid Expense and Other Assets Proceeds from borrowings under credit facility and term loans Proceeds from Long-Term Lines of Credit Adjustments to reconcile net income to net cash provided by (used in) operating activities: Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity [Abstract] Risk adjustments liability Amounts Due to Government Agencies, Risk Adjustment and Part D risk sharing Amounts Due to Government Agencies, Risk Adjustment and Part D risk sharing Financing activities: Cash Provided by (Used in) Financing Activity, Including 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Basis Of Presentation [Line Items] Basis Of Presentation [Line Items] Entity Interactive Data Current Entity Interactive Data Current Compensation Actually Paid vs. Other Measure Compensation Actually Paid vs. Other Measure [Text Block] Due after one year through five years Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, after Year One Through Five Accounts payable, accrued liabilities and other Accounts Payable and Accrued Liabilities, Current Entity Small Business Entity Small Business Comprehensive (loss) income Comprehensive Income (Loss), Net of Tax, Attributable to Parent Termination Date Trading Arrangement Termination Date Property, Plant, and Equipment [Line Items] Property, Plant, and Equipment [Line Items] Fair Value Measurements, Recurring and Nonrecurring [Table] Fair Value, Recurring and Nonrecurring [Table] Compensation Actually Paid vs. Total Shareholder Return Compensation Actually Paid vs. Total Shareholder Return 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Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid Stock-based compensation (in shares) Weighted Average Number Of Shares, Share Based Compensation Weighted Average Number Of Shares, Share Based Compensation Concentrations of Credit Risk Concentration Risk, Credit Risk, Policy [Policy Text Block] Stock Price or TSR Estimation Method Stock Price or TSR Estimation Method [Text Block] Entity Tax Identification Number Entity Tax Identification Number Percent due to Medicare, medical loss ratio Percent Due To Government Agencies, Medicare, Medical Loss Ratio And Profit Sharing, Threshold Percent Due To Government Agencies, Marketplace, Medical Loss Ratio And Profit Sharing, Threshold Debt Instrument Covenant Period [Domain] Debt Instrument Covenant Period [Domain] Debt Instrument Covenant Period [Domain] Cash, cash equivalents, and restricted cash and cash equivalents at beginning of period Cash, cash equivalents, and restricted cash and cash equivalents at end of period 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compensation Share-Based Payment Arrangement, Noncash Expense New Credit Agreement New Credit Agreement [Member] New Credit Agreement Due after five years through ten years Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, after Year 5 Through 10 Long-term Debt, Type [Domain] Long-Term Debt, Type [Domain] Net income per share - basic (in dollars per share) Earnings Per Share, Basic Covenant Period One Covenant Period One [Member] Covenant Period One Common stock purchases Payments for Repurchase of Common Stock Deferred revenue Contract with Customer, Liability, Current Mortgage-backed securities Collateralized Mortgage-Backed Securities [Member] Total current assets Assets, Current Statistical Measurement [Axis] Statistical Measurement [Axis] Insider Trading Arrangements [Line Items] Long-term debt Total Long-Term Debt, Excluding Current Maturities Award Type Award Type [Axis] Named Executive Officers, Footnote Named Executive Officers, Footnote [Text Block] Amortized Cost Debt Securities, Available-for-Sale, Amortized Cost, Excluding Accrued Interest, after Allowance for Credit Loss Retained earnings Retained Earnings (Accumulated Deficit) Product and Service [Axis] Product and Service [Axis] Stock purchases (in shares) Weighted Average Number of Shares, Common Stock Subject to Repurchase or Cancellation Aggregate Change in Present Value of Accumulated Benefit for All Pension Plans Reported in Summary Compensation Table Aggregate Change in Present Value of Accumulated Benefit for All Pension Plans Reported in Summary Compensation Table [Member] Awards Close in Time to MNPI Disclosures Awards Close in Time to MNPI Disclosures [Table] Debt Instrument Covenant Period [Axis] Debt Instrument Covenant Period [Axis] Debt Instrument Covenant Period Common Stock Common Stock [Member] Fair Value Measurement [Domain] Fair Value Measurement [Domain] Health Plans Health Plans [Member] Health plans. Compensation Actually Paid vs. Company Selected Measure Compensation Actually Paid vs. Company Selected Measure [Text Block] Cover [Abstract] Cover [Abstract] Risk adjustment receivable (payable) Affordable Care Act, Premium Stabilization Program, Risk Adjustment, (Payable) Affordable Care Act, Premium Stabilization Program, Risk Adjustment, Receivable (Payable) Insurance [Abstract] Risk adjustment, net receivable (payable) Affordable Care Act, Premium Stabilization Program, Risk Adjustment, Net Receivable Affordable Care Act, Premium Stabilization Program, Risk Adjustment, Receivable (Payable) Receivables Receivable [Policy Text Block] Minimum MLR, medical cost corridors and profit sharing liability Medical Premiums Liability, Medical Care Costs Threshold Medical Premiums Liability, Medical Care Costs Threshold Equity Awards Adjustments Equity Awards Adjustments [Member] Total liabilities and stockholders’ equity Liabilities and Equity Goodwill, and intangible assets, net Intangible Asset, Including Goodwill, after Accumulated Amortization Government agencies liability Amounts Due To Government Agencies, Medicare, Medical Loss Ratio And Profit Sharing, Threshold Amounts Due To Government Agencies, Medicare, Medical Loss Ratio And Profit Sharing, Threshold Employee Stock Option Share-Based Payment Arrangement, Option [Member] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Segments [Axis] Segments [Axis] Additional 402(v) Disclosure Additional 402(v) Disclosure [Text Block] Tabular List, Table Tabular List [Table Text Block] Debt Long-Term Debt [Text Block] Other Other Operating Income (Expense), Net Name Awards Close in Time to MNPI Disclosures, Individual Name Medicaid Medicaid [Member] Medicaid Amortized cost, due after five years Debt Securities, Held-to-Maturity, Amortized Cost, after Allowance for Credit Loss, Maturity, Allocated and Single Maturity Date, after Year 5 through 10 Year-end Fair Value of Equity Awards Granted in Covered Year that are Outstanding and Unvested Year-end Fair Value of Equity Awards Granted in Covered Year that are Outstanding and Unvested [Member] Amounts due government agencies Increase (Decrease) In Medical Premium Liability Due To Agency Increase (Decrease) in Medical Premium Liability Due to Agency General and administrative expenses General and Administrative Expense Preferred stock, shares authorized (in shares) Preferred Stock, Shares Authorized Receivables Receivables, Net, Current Property, Plant, and Equipment [Table] Property, Plant, and Equipment [Table] Preferred stock, $0.001 par value; 20 million shares authorized, no shares issued and outstanding Preferred Stock, Value, Issued Adjustment to Compensation: Adjustment to Compensation [Axis] Mortgage-backed securities Commercial Mortgage-Backed Securities [Member] Rule 10b5-1 Arrangement Terminated Rule 10b5-1 Arrangement Terminated [Flag] Aggregate Erroneous Compensation Amount Aggregate Erroneous Compensation Amount Statement of Cash Flows [Abstract] Statement of Cash Flows [Abstract] Credit Facility [Axis] Credit Facility [Axis] Aggregate Available Trading Arrangement, Securities Aggregate Available Amount Total assets Assets, Fair Value Disclosure Name Measure Name Insurance Claims Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward] Payments for medical care costs related to: Payments For Medical Care Costs [Abstract] Payments for medical care costs. Pay vs Performance Disclosure [Line Items] Fair Value Hierarchy and NAV [Domain] Fair Value Hierarchy and NAV [Domain] In a continuous loss position for less than 12 Months, total number of positions Debt Securities, Available-for-Sale, Continuous Unrealized Loss Position, Less than 12 Months, Number of Positions Debt Instrument [Line Items] Debt Instrument [Line Items] Pay vs Performance Disclosure Pay vs Performance Disclosure [Table] Additional Paid-in Capital Additional Paid-in Capital [Member] Entity Filer Category Entity Filer Category Other Other Securities [Member] Other Securities Maturity period (less than) Investments, Maturity Period Investments, Maturity Period Name Trading Arrangement, Individual Name Cash and cash equivalents Cash and cash equivalents Cash and Cash Equivalent Company Selected Measure Amount Company Selected Measure Amount Investments, Debt and Equity Securities [Abstract] Investments, Debt and Equity Securities [Abstract] Depreciation and amortization Depreciation, Depletion and Amortization Entity Address, Address Line Two Entity Address, Address Line Two Share-based compensation (in shares) Shares Issued, Shares, Share-Based Payment Arrangement, after Forfeiture Current assets: Assets, Current [Abstract] Non-PEO NEO Non-PEO NEO [Member] Senior Notes Senior Notes [Member] Entity Address, Address Line One Entity Address, Address Line One Remaining intangible assets Intangible Asset, Finite-Lived, Impairment Loss Income tax expense Income Tax Expense (Benefit) Effect of dilutive securities: Dilutive Securities, Effect on Basic Earnings Per Share [Abstract] Medical care costs Medical care costs Cost of Product and Service Sold Award Timing Method Award Timing Method [Text Block] Net increase (decrease) in cash, cash equivalents, and restricted cash and cash equivalents Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Period Increase (Decrease), Including Exchange Rate Effect and Discontinued Operation Segment expenses Segment Expenses Segment Expenses Forgone Recovery, Explanation of Impracticability Forgone Recovery, Explanation of Impracticability [Text Block] Contract Rights and Licensing Agreements Contract Rights and Licenses [Member] Contract Rights and Licenses Net income Net income Net income Net Income (Loss) Attributable to Parent Long-term Debt, Type [Axis] Long-Term Debt, Type [Axis] Erroneous Compensation Analysis Erroneous Compensation Analysis [Text Block] Statement [Table] Statement [Table] Restatement Determination Date: Restatement Determination Date [Axis] Receivables Increase (Decrease) in Receivables Covenant Period Two Covenant Period Two [Member] Covenant Period Two Revenue from external customers Premiums Earned And Service Revenue Premiums Earned And Service Revenue Revenue: Revenues [Abstract] U.S. Treasury notes US Treasury Notes Securities [Member] Pension Benefits Adjustments, Footnote Pension Benefits Adjustments, Footnote [Text Block]