Other Liabilities Disclosure [Abstract] Liability for Claims and Claims Adjustment Expense [Table] Liability for Claims and Claims Adjustment Expense [Table] Customer [Axis] Customer [Axis] Customer [Domain] Customer [Domain] CMS Subsidies CMS Subsidies [Member] CMS Subsidies [Member] Liability for Claims and Claims Adjustment Expense [Line Items] Liability for Claims and Claims Adjustment Expense [Line Items] Operating expense Disposal Group, Including Discontinued Operation, Operating Expense Insurance Claims Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward] Medical claims and benefits payable, beginning balance Liability for Claims and Claims Adjustment Expense Components of medical care costs related to: Components Of Medical Care Costs [Abstract] Components of medical care costs. Current period Current Year Claims and Claims Adjustment Expense Prior periods Prior Year Claims and Claims Adjustment Expense Total medical care costs Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims Change in non-risk provider payables Medical Claims And Benefits Payable, Adjustments, Change In Provider Medical Claims and Benefits Payable, Adjustments, Change in Provider Payments for medical care costs related to: Payments For Medical Care Costs [Abstract] Payments for medical care costs. Current period Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Current Year Prior periods Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Prior Years Total paid Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid Medical claims and benefits payable, ending balance Investments, Debt and Equity Securities [Abstract] Investments Investments in Debt and Marketable Equity Securities (and Certain Trading Assets) Disclosure [Text Block] Earnings Per Share [Abstract] Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table] Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table] Debt Instrument [Axis] Debt Instrument [Axis] Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] 1.625% Notes 1.625% Notes [Member] 1.625% Notes [Member] Class of Warrant or Right [Axis] Class of Warrant or Right [Axis] Class of Warrant or Right [Domain] Class of Warrant or Right [Domain] 1.125% Warrants Cash Convertible Senior Notes Due 2020, Warrants [Member] Cash Convertible Senior Notes Due 2020, Warrants [Member] Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Numerator: Net Income (Loss) Available to Common Stockholders, Basic [Abstract] Net income Net Income (Loss) Attributable to Parent Denominator: Weighted Average Number of Shares Outstanding Reconciliation [Abstract] Shares outstanding at the beginning of the period (in shares) Shares, Outstanding Exchange of 1.625% Notes (in shares) Weighted Average Number of Shares Issued, Basic Denominator for basic net income per share (in shares) Weighted Average Number of Shares Outstanding, Basic Effect of dilutive securities: Dilutive Securities, Effect on Basic Earnings Per Share [Abstract] 1.125% Warrants (in shares) Incremental Common Shares Attributable to Dilutive Effect of Call Options and Warrants 1.625% Notes (in shares) Incremental Common Shares Attributable to Dilutive Effect of Conversion of Debt Securities Stock-based compensation (in shares) Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements Denominator for diluted net income per share (in shares) Weighted Average Number of Shares Outstanding, Diluted Net income per share: Earnings Per Share, Basic and Diluted [Abstract] Basic (in dollars per share) Earnings Per Share, Basic Diluted (in dollars per share) Earnings Per Share, Diluted Potentially dilutive common shares excluded from calculations: (1) Potentially Dilutive Common Shares Excluded From Calculations [Abstract] Potentially Dilutive Common Shares Excluded From Calculations [Abstract] Stock-based compensation (in shares) Antidilutive Securities Excluded from Computation of EPS, Share Based Compensation, Amount Antidilutive Securities Excluded from Computation of EPS, Share Based Compensation, Amount Stated percentage of warrants Class Of Warrant Or Right, Stated Interest Rate Class Of Warrant Or Right, Stated Interest Rate Accounting Policies [Abstract] Significant Accounting Policies Significant Accounting Policies [Text Block] Leases [Abstract] Lessee, Lease, Description [Table] Lessee, Lease, Description [Table] Range [Axis] Range [Axis] Range [Domain] Range [Domain] Minimum Minimum [Member] Maximum Maximum [Member] Lessee, Lease, Description [Line Items] Lessee, Lease, Description [Line Items] Operating lease term Lessee, Operating Lease, Term of Contract Operating lease renewal term Lessee, Operating Lease, Renewal Term Finance lease term Lessee, Finance Lease, Term of Contract Finance lease renewal term Lessee, Finance Lease, Renewal Term Segment Reporting [Abstract] Number of reportable segments (in segment) Number of Reportable Segments Operating Leases Operating Lease Liabilities, Payments Due [Abstract] 2019 Lessee, Operating Lease, Liability, Payments, Remainder of Fiscal Year 2020 Lessee, Operating Lease, Liability, Payments, Due Year Two 2021 Lessee, Operating Lease, Liability, Payments, Due Year Three 2022 Lessee, Operating Lease, Liability, Payments, Due Year Four 2023 Lessee, Operating Lease, Liability, Payments, Due Year Five Thereafter Lessee, Operating Lease, Liability, Payments, Due after Year Five Total lease payments Lessee, Operating Lease, Liability, Payments, Due Less imputed interest Lessee, Operating Lease, Liability, Undiscounted Excess Amount Total operating lease liabilities Operating Lease, Liability Finance Leases Finance Lease Liabilities, Payments, Due [Abstract] 2019 Finance Lease, Liability, Payments, Remainder of Fiscal Year 2020 Finance Lease, Liability, Payments, Due Year Two 2021 Finance Lease, Liability, Payments, Due Year Three 2022 Finance Lease, Liability, Payments, Due Year Four 2023 Finance Lease, Liability, Payments, Due Year Five Thereafter Finance Lease, Liability, Payments, Due after Year Five Total lease payments Finance Lease, Liability, Payments, Due Less imputed interest Finance Lease, Liability, Undiscounted Excess Amount Total finance lease liabilities Finance Lease, Liability Leases Lessee, Operating Leases [Text Block] Leases Lessee, Finance Leases [Text Block] Schedule of Available-for-sale Securities Schedule of Available-for-sale Securities [Table] Financial Instrument [Axis] Financial Instrument [Axis] Financial Instruments [Domain] Financial Instruments [Domain] Corporate debt securities Corporate Debt Securities [Member] GSEs US Government-sponsored Enterprises Debt Securities [Member] Municipal securities Municipal Securities [Member] Municipal securities. Asset-backed securities Asset-backed Securities [Member] Debt Securities, Available-for-sale [Line Items] Debt Securities, Available-for-sale [Line Items] In a Continuous Loss Position for Less than 12 Months, Estimated Fair Value Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months In a Continuous Loss Position for Less than 12 Months, Unrealized Losses Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss In a Continuous Loss Position for Less than 12 Months, Number of Positions (in security) Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Number of Positions In a Continuous Loss Position for 12 Months or More, Estimated Fair value Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer In a Continuous Loss Position for 12 Months or More, Unrealized Losses Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss In a Continuous Loss Position for 12 Months or More, Number of Positions (in security) Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Number of Positions Organization, Consolidation and Presentation of Financial Statements [Abstract] Organization and Basis of Presentation Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block] Stockholders' Equity Note [Abstract] Schedule of Deferred Compensation Arrangement with Individual, Share-based Payments [Table] Schedule of Deferred Compensation Arrangement with Individual, Share-based Payments [Table] Award Type [Axis] Award Type [Axis] Equity Award [Domain] Equity Award [Domain] Restricted Stock Awards Restricted Stock [Member] Performance Stock Units Restricted Stock Units (RSUs) [Member] Performance Stock Awards Performance Shares [Member] Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items] Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items] Number of Shares Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] Beginning Balance (shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number Granted (shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period Vested (shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period Forfeited (shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period Ending Balance (shares) Weighted Average Grant Date Fair Value Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract] Begining Balance (usd per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value Granted (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 Vested (usd per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value Forfeited (usd per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value Ending Balance (usd per share) Schedule of Stock by Class [Table] Schedule of Stock by Class [Table] Subsequent Event Type [Axis] Subsequent Event Type [Axis] Subsequent Event Type [Domain] Subsequent Event Type [Domain] Subsequent Event Subsequent Event [Member] Class of Stock [Axis] Class of Stock [Axis] Class of Stock [Domain] Class of Stock [Domain] Common Stock Common Stock [Member] Employee Stock Option Employee Stock Option [Member] Class of Stock [Line Items] Class of Stock [Line Items] Number of warrants issued (in shares) Debt Conversion, Converted Instrument, Warrants or Options Issued Warrant, strike price per share (in dollars per share) Class of Warrant or Right, Exercise Price of Warrants or Rights Warrants outstanding (in shares) Class of Warrant or Right, Outstanding Cash paid for partial termination of 1.125% Warrants Payments for Repurchase of Warrants Number of warrants terminated (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Terminated, Number Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Terminated, Number Number of common stock issued (in shares) Stock Issued During Period, Shares, Share-based Compensation, Net of Forfeitures Share-based compensation Share-based Compensation Unrecognized compensation expense Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized Weighted average period for recognition Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition Unrecognized compensation forfeiture rate Unrecognized Compensation Forfeited Rate Unrecognized compensation forfeited rate. Stock options granted (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross Stock options exercised (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period Fair Value Disclosures [Abstract] Fair value of assets measured on recurring basis Fair Value, Assets Measured on Recurring Basis [Table Text Block] Schedule of fair value, asset and liabilities measured on recurring basis - disclosure only Schedule Of Fair Value, Asset And Liabilities Measured On Recurring Basis [Table Text Block] Schedule of Fair Value, Asset and Liabilities Measured on Recurring Basis [Table Text Block] Statement of Cash Flows [Abstract] Statement Statement [Table] Long-term Debt, Type [Axis] Long-term Debt, Type [Axis] Long-term Debt, Type [Domain] Long-term Debt, Type [Domain] Convertible Notes Convertible Debt [Member] 1.625% Notes Convertible Senior Notes Due 2044 [Member] Convertible Senior Notes Due 2044 [Member] Derivative Instrument [Axis] Derivative Instrument [Axis] Derivative Contract [Domain] Derivative Contract [Domain] 1.125% Call Option Call Option, Derivative Asset [Member] Call Option, Derivative Asset [Member] 1.125% Conversion Option Embedded Derivative Financial Instruments [Member] Statement [Line Items] Statement [Line Items] Percentage of contractual interest rate on derivative Derivative, Fixed Interest Rate Percentage of contractual interest rate Debt Instrument, Interest Rate, Stated Percentage Fair Value, by Balance Sheet Grouping [Table] Fair Value, by Balance Sheet Grouping [Table] Balance Sheet Location [Axis] Balance Sheet Location [Axis] Balance Sheet Location [Domain] Balance Sheet Location [Domain] Current liabilities: Derivative liability Current Liabilities [Member] Current Liabilities [Member] 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 Amount Reported Value Measurement [Member] Fair Value Estimate of Fair Value Measurement [Member] Senior Notes Senior Notes [Member] Credit Facility Revolving Credit Facility [Member] 5.375% Notes Senior Notes Due 2022 [Member] Senior Notes Due 2022 [Member] 4.875% Notes 4.875% Senior Notes [Member] 4.875% Senior Notes [Member] 1.125% Convertible Notes Cash Convertible Senior Notes due 2020 [Member] Cash Convertible Senior Notes due 2020 [Member] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Percentage of contractual interest rate on Notes Fair value of debt Debt Instrument, Fair Value Disclosure Derivative liabilities Derivative Liability, Fair Value, Gross Liability Net Income per Share Earnings Per Share [Text Block] Schedule Of Premium Revenue By Health Plan Type Schedule of Premium Revenue by Health Plan Type [Table] Schedule of premium revenue by health plan type. Adjustments for New Accounting Pronouncements [Axis] Adjustments for New Accounting Pronouncements [Axis] Type of Adoption [Domain] Type of Adoption [Domain] ASU 2014-09 Accounting Standards Update 2014-09 [Member] Equity Components [Axis] Equity Components [Axis] Equity Component [Domain] Equity Component [Domain] Retained Earnings Retained Earnings [Member] Product and Service [Axis] Product and Service [Axis] Product and Service [Domain] Product and Service [Domain] Medicaid Expansion Medicaid Expansion [Member] Medicaid Expansion [Member] Schedule of Premium Revenue by Health Plan Type [Line Items] Schedule of Premium Revenue by Health Plan Type [Line Items] Schedule of premium revenue by health plan type. Medical cost floors and corridors Amounts Due to Government Agencies, Medical Cost Floors and Corridors Amounts Due to Government Agencies, Medical Cost Floors and Corridors Amounts due government agencies Medical Premium Liability Due To Agency Medical Premium Liability Due to Agency Risk adjustment payable Affordable Care Act, Premium Stabilization Program, Risk Adjustment, (Payable) Affordable Care Act, Premium Stabilization Program, Risk Adjustment, (Payable) Risk adjustment receivable Affordable Care Act, Premium Stabilization Program, Risk Adjustment, Receivable Affordable Care Act, Premium Stabilization Program, Risk Adjustment, Receivable Maturity period Investments, Maturity Period Investments, Maturity Period Restricted cash and cash equivalents Restricted Cash and Cash Equivalents Adoption of ASU Cumulative Effect of New Accounting Principle in Period of Adoption Document and Entity Information [Abstract] -- None. No documentation exists for this element. -- 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 Document Type Document Type Document Period End Date Document Period End Date Document Fiscal Year Focus Document Fiscal Year Focus Document Fiscal Period Focus Document Fiscal Period Focus Amendment Flag Amendment Flag Entity Emerging Growth Company Entity Emerging Growth Company Entity Small Business Entity Small Business Trading Symbol Trading Symbol Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Derivative Instruments and Hedging Activities Disclosure [Abstract] Schedule of Derivative Instruments in Statement of Financial Position, Fair Value Schedule of Derivative Instruments in Statement of Financial Position, Fair Value [Table Text Block] Segments Segment Reporting Disclosure [Text Block] Debt Disclosure [Abstract] Debt Long-term Debt [Text Block] Lease Cost Lease, Cost [Table Text Block] Supplemental Lease Information Assets And Liabilities, Lessee [Table Text Block] Assets And Liabilities, Lessee [Table Text Block] Operating Lease Maturities Lessee, Operating Lease, Liability, Maturity [Table Text Block] Finance Lease Maturities Finance Lease, Liability, Maturity [Table Text Block] Statement of Financial Position [Abstract] Current assets: Assets, Current [Abstract] Cash and cash equivalents Cash and Cash Equivalents, at Carrying Value Investments Marketable Securities, Current Receivables Receivables, Net, Current Prepaid expenses and other current assets Prepaid Expense and Other Assets, Current Derivative asset Derivative Asset, Current Total current assets Assets, Current Property, equipment, and capitalized software, net Property, Plant and Equipment, Net Goodwill and intangible assets, net Intangible Assets, Net (Including Goodwill) Restricted investments Restricted Investments, Noncurrent Deferred income taxes Deferred Income Tax Assets, Net Other assets Other Assets, Noncurrent Total assets Assets Current liabilities: Liabilities, Current [Abstract] Medical claims and benefits payable Accounts payable and accrued liabilities Accounts Payable and Accrued Liabilities, Current Deferred revenue Contract with Customer, Liability, Current Current portion of long-term debt Long-term Debt and Capital Lease Obligations, Current Derivative liability Derivative Liability, Current Total current liabilities Liabilities, Current Long-term debt Long-term Debt, Excluding Current Maturities Finance lease liabilities Finance Lease, Liability, Noncurrent Other long-term liabilities Other Liabilities, Noncurrent Total liabilities Liabilities Stockholders’ equity: Stockholders' Equity Attributable to Parent [Abstract] Common stock, $0.001 par value, 150 million shares authorized; outstanding: 63 million shares at March 31, 2019 and 62 million shares at December 31, 2018 Common Stock, Value, Outstanding Preferred stock, $0.001 par value; 20 million shares authorized, no shares issued and outstanding Preferred Stock, Value, Issued Additional paid-in capital Additional Paid in Capital, Common Stock Accumulated other comprehensive loss Accumulated Other Comprehensive Income (Loss), Net of Tax Retained earnings Retained Earnings (Accumulated Deficit) Total stockholders’ equity Stockholders' Equity Attributable to Parent Total liabilities and stockholders' equity Liabilities and Equity Fair Value Measurements, Recurring and Nonrecurring Fair Value Measurements, Recurring and Nonrecurring [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] Observable Inputs (Level 1) Fair Value, Inputs, Level 1 [Member] Directly or Indirectly Observable Inputs (Level 2) Fair Value, Inputs, Level 2 [Member] Unobservable Inputs (Level 3) Fair Value, Inputs, Level 3 [Member] U.S. Treasury notes US Treasury Notes Securities [Member] Government-sponsored enterprise securities (“GSEs”) Mortgage-backed securities Commercial Mortgage Backed Securities [Member] Certificate of deposit Certificates of Deposit [Member] Other Other Investments [Member] Subtotal - current investments Current Investments [Member] Current Investments [Member] 1.125% Call Option derivative asset Derivative Financial Instruments, Assets [Member] 1.125% Conversion Option derivative liability 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] Total assets measured at fair value on a recurring basis Assets, Fair Value Disclosure 1.125% Conversion Option derivative liability Derivative Liability Total liability measured at fair value on a recurring basis Financial and Nonfinancial Liabilities, Fair Value Disclosure Percentage of contractual interest rate on Call Option Schedule of Long-term Debt Instruments Schedule of Long-term Debt Instruments [Table] Line of Credit Line of Credit [Member] Credit Facility [Axis] Credit Facility [Axis] Credit Facility [Domain] Credit Facility [Domain] Credit Facility Letter of Credit Letter of Credit [Member] Term Loan Term Loan [Member] Term Loan [Member] Debt Instrument [Line Items] Debt Instrument [Line Items] Maximum borrowing capacity Line of Credit Facility, Maximum Borrowing Capacity Minimum principal amount of advancements Line of Credit Facility, Minimum Threshold for Advancements Line of Credit Facility, Minimum Threshold for Advancements Amortization payment percentage Line of Credit Facility, Amortization Payment Percentage Line of Credit Facility, Amortization Payment Percentage Aggregate principal amount of notes outstanding Long-term Debt, Gross Current borrowing capacity Line of Credit Facility, Remaining Borrowing Capacity Amount outstanding under Letter of Credit Long-term Line of Credit Face amount Debt Instrument, Face Amount Repayments of principal Debt Instrument, Periodic Payment, Principal Repayment of aggregate carrying amount Debt Instrument, Periodic Payment Repayments of debt Repayments of Debt Loss on debt extinguishment Gain (Loss) on Extinguishment of Debt Conversion ratio Debt Instrument, Convertible, Conversion Ratio Conversion price per share of common stock (in dollars per share) Debt Instrument, Convertible, Conversion Price Effective interest percentage Debt Instrument, Interest Rate, Effective Percentage Remaining amortization period (less than) Debt Instrument, Convertible, Remaining Discount Amortization Period If-converted value Debt Instrument, Convertible, If-converted Value in Excess of Principal Proceeds from borrowings under Term Loan Proceeds from Long-term Lines of Credit Fair Value Measurements Fair Value Disclosures [Text Block] Total cash, cash equivalents, and restricted cash and cash equivalents presented in the statements of cash flows Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents 2020 Long-term Debt, Maturities, Repayments of Principal, Remainder of Fiscal Year 2021 Long-term Debt, Maturities, Repayments of Principal in Year Two 2022 Long-term Debt, Maturities, Repayments of Principal in Year Three 2023 Long-term Debt, Maturities, Repayments of Principal in Year Four 2024 Long-term Debt, Maturities, Repayments of Principal in Year Five Thereafter Long-term Debt, Maturities, Repayments of Principal after Year Five Long-term Debt, Gross Equity [Abstract] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Total fair value of awards granted Share-Based Compensation Arrangement By Share-Based Payment Award, Equity Instruments Other Than Options, Granted In Period, Fair Value Share-Based Compensation Arrangement By Share-Based Payment Award, Equity Instruments Other Than Options, Granted In Period, Fair Value Total fair value of awards vested Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value Convertible Notes Current portion of long-term debt: Debt, Current [Abstract] Debt net of unamortized discount Long-Term Debt, Current Maturities, Net Of Unamortized Premium (Discount) Long-Term Debt, Current Maturities, Net Of Unamortized Premium (Discount) Lease financing obligations Capital Lease Obligations, Current Debt issuance costs Debt Issuance Costs, Current, Net Current portion of long-term debt Non-current portion of long-term debt: Long-term Debt, Excluding Current Maturities [Abstract] Debt net of unamortized debt discount Long-Term Debt, Noncurrent, Net Of Unamortized Debt Discount Long-Term Debt, Noncurrent, Net Of Unamortized Debt Discount Debt issuance costs Debt Issuance Costs, Noncurrent, Net Senior notes Other amounts due to states Amounts Due to Government Agencies, Amounts Due State Amounts Due to Government Agencies, Amounts Due State Risk adjustment Amounts Due to Government Agencies, Risk Adjustment Amounts Due to Government Agencies, Risk Adjustment Cost sharing reduction Amounts Due to Government Agencies, Cost Sharing Reduction Amounts Due to Government Agencies, Cost Sharing Reduction Other Amounts Due to Government Agencies, Other Amounts Due to Government Agencies, Other Medical Premium Liability Due To Agency Restructuring and Related Activities [Abstract] Restructuring Costs Restructuring and Related Activities Disclosure [Text Block] Medical Claims and Benefits Payable Medical Claims And Benefits Payable [Text Block] Medical claims and benefits payable. Derivative Derivative [Table] Current assets: Derivative asset Current Assets [Member] Current Assets [Member] Derivative [Line Items] Derivative [Line Items] Derivative assets Derivative Asset, Fair Value, Gross Asset Cash received for partial termination of 1.125% Call Option Proceeds from Convertible Debt Debt conversion, net cash receipts Debt Conversion, Converted Instrument, Amount Common stock, par value (usd per share) Common Stock, Par or Stated Value Per Share Common stock, shares authorized (in shares) Common Stock, Shares Authorized Common stock, shares outstanding (in shares) Common Stock, Shares, Outstanding Preferred stock, par value (usd per share) Preferred Stock, Par or Stated Value Per Share Preferred stock, shares authorized (in shares) Preferred Stock, Shares Authorized Preferred stock, shares issued (in shares) Preferred Stock, Shares Issued Preferred stock, shares outstanding (in shares) Preferred Stock, Shares Outstanding Schedule of maturities of long-term debt Schedule of Maturities of Long-term Debt [Table Text Block] Long term debt Schedule of Long-term Debt Instruments [Table Text Block] Interest Costs Schedule Of Debt Instruments Interest Cost Recognized [Table Text Block] Schedule of debt instruments interest cost recognized. Summary of denominators for the computation of basic and diluted net income (loss) per share Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Statement of Stockholders' Equity [Abstract] Operating segment information Schedule of Segment Reporting Information, by Segment [Table Text Block] Due in one year or less Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, within One Year, Amortized Cost Contractual interest at coupon rate Interest Expense, Debt, Excluding Amortization Amortization of the discount Amortization of Debt Discount (Premium) Interest expense, debt Interest Expense, Debt Statement of Comprehensive Income [Abstract] Other comprehensive income (loss): Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract] Unrealized investment gain (loss) Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, before Tax Less: effect of income taxes 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 Income Statement [Abstract] Revenue from External Customers by Products and Services [Table] Revenue from External Customers by Products and Services [Table] Health Care, Premium Health Care, Premium [Member] Technology Service Technology Service [Member] Revenue from External Customer [Line Items] Revenue from External Customer [Line Items] Revenue: Revenues [Abstract] Premium revenue Premiums Earned, Net Premium tax revenue Health Care Organization, Premium Tax Revenue Health Care Organization, Premium Tax Revenue Health insurer fees reimbursed Health Care Organization, Insurer Fee Revenue Health Care Organization, Insurer Fee Revenue Service revenue Insurance Services Revenue Investment income and other revenue Interest and Dividend Income, Operating Total revenue Revenues Operating expenses: Costs and Expenses [Abstract] Cost of revenue Cost of Goods and Services Sold General and administrative expenses General and Administrative Expense Premium tax expenses Premium Tax Expenses An assessment levied by a state government on the net premium income collected. Health insurer fees Health Care Organization, Insurer Fee Expense Health Care Organization, Insurer Fee Expense Depreciation and amortization Depreciation, Depletion and Amortization, Nonproduction Restructuring costs Restructuring Costs Total operating expenses Costs and Expenses Operating income Operating Income (Loss) Other expenses, net: Nonoperating Income (Expense) [Abstract] Interest expense Interest Expense Other (income) expenses, net Other Nonoperating Income (Expense) Total other expenses, net Nonoperating Income (Expense) Income before income tax expense Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest Income tax expense Income Tax Expense (Benefit) Net income Additional Paid-in Capital Additional Paid-in Capital [Member] Accumulated Other Comprehensive Loss AOCI Attributable to Parent [Member] ASU 2016-02 Accounting Standards Update 2016-02 [Member] Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Beginning Balance (in shares) Beginning Balance Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest Partial termination of 1.125% Warrants Adjustments to Additional Paid in Capital, Other Exchange of 1.625% Convertible Notes (in shares) Stock Issued During Period, Shares, Conversion of Convertible Securities Exchange of 1.625% Convertible Notes Adjustments to Additional Paid in Capital, Convertible Debt with Conversion Feature Other comprehensive gain (loss), net Share-based compensation (in shares) Share-based compensation Stock Issued During Period, Value, Share-based Compensation, Net of Forfeitures Ending Balance (in shares) Ending Balance Operating leases Lessee, Operating Lease, Description [Abstract] Other assets Operating Lease, Right-of-Use Asset Accounts payable and accrued liabilities Operating Lease, Liability, Current Other long-term liabilities Operating Lease, Liability, Noncurrent Total operating lease liabilities Finance leases Lessee, Finance Lease, Description [Abstract] Property, equipment, and capitalized software, net Finance Lease, Right-of-Use Asset Accounts payable and accrued liabilities Finance Lease, Liability, Current Finance lease liabilities Total finance lease liabilities Weighted average remaining lease term Weighted Average Remaining Lease Term [Abstract] Weighted Average Remaining Lease Term [Abstract] Operating leases Operating Lease, Weighted Average Remaining Lease Term Finance leases Finance Lease, Weighted Average Remaining Lease Term Weighted average discount rate Weighted Average Discount Rate [Abstract] Weighted Average Discount Rate [Abstract] Operating leases Operating Lease, Weighted Average Discount Rate, Percent Finance leases Finance Lease, Weighted Average Discount Rate, Percent Schedule of Restructuring and Related Costs [Table] Schedule of Restructuring and Related Costs [Table] Restructuring Type [Axis] Restructuring Type [Axis] Type of Restructuring [Domain] Type of Restructuring [Domain] One-Time Termination Benefits One-time Termination Benefits [Member] Consulting Fees Professional Services Fees [Member] Professional Services Fees [Member] Other Restructuring Costs Other Restructuring [Member] Contract Termination Contract Termination [Member] Segments [Axis] Segments [Axis] Segments [Domain] Segments [Domain] Other segment Other Segments [Member] Restructuring Plan [Axis] Restructuring Plan [Axis] Restructuring Plan [Domain] Restructuring Plan [Domain] IT Restructuring IT Restructuring [Member] IT Restructuring [Member] 2017 Restructuring Plan 2017 Restructuring Plan [Member] 2017 Restructuring Plan [Member] Restructuring Cost and Reserve [Line Items] Restructuring Cost and Reserve [Line Items] Expected restructuring costs Restructuring and Related Cost, Expected Cost Remaining Decrease to estimated expected costs remaining Restructuring and Related Cost, Expected Cost Remaining, Decrease to Previous Estimate Restructuring and Related Cost, Expected Cost Remaining, Decrease to Previous Estimate Restructuring Reserve Restructuring Reserve U.S. Treasury notes Mortgage-backed securities Other Other Financial Instruments [Member] Other Financial Instruments [Member] Restricted Cash and Cash Equivalents [Axis] Restricted Cash and Cash Equivalents [Axis] Cash and Cash Equivalents [Domain] Cash and Cash Equivalents [Domain] 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 Cash and Cash Equivalents Restrictions on Cash and Cash Equivalents [Table Text Block] Schedule of Cash and Cash Equivalents Schedule of Cash and Cash Equivalents [Table Text Block] Quality incentive premium revenue recognized Quality Incentive Premium Revenue Recognized [Table Text Block] Quality incentive premium revenue recognized. Amounts due to government agencies Reserves Reported to Other Agencies [Table Text Block] Fee-for-service claims incurred but not paid (“IBNP”) Liability for Unpaid Claims and Claims Adjustment Expense, Incurred but Not Paid (IBNP), Fee-for-service Claims, Amount Liability for Unpaid Claims and Claims Adjustment Expense, Incurred but Not Paid (IBNP), Fee-for-service Claims, Amount Pharmacy payable Pharmacy Claims Payable Pharmacy Claims Payable Capitation payable Capitation Claims Payable Capitation Claims Payable Other Other Claims Payable Other Claims Payable Medical claims and benefits payable Non-risk provider payables Medical Claims And Benefits Payable Medical Claims and Benefits Payable Expense (recovery) for prior period claims development Investments Debt Securities, Available-for-sale [Table Text Block] Contractual maturities of investments Investments Classified by Contractual Maturity Date [Table Text Block] Stockholders' Equity Stockholders' Equity Note Disclosure [Text Block] Cash used in operating activities: Net Cash Provided by (Used in) Operating Activities [Abstract] Operating leases Operating Lease, Payments Finance leases Finance Lease, Interest Payment on Liability Cash used in financing activities: Net Cash Provided by (Used in) Financing Activities [Abstract] Finance leases Finance Lease, Principal Payments ROU assets recognized in exchange for lease obligations: Right-of-Use Asset Obtained in Exchange for Operating Lease Liability [Abstract] Right-of-Use Asset Obtained in Exchange for Operating Lease Liability [Abstract] Operating leases Right-of-Use Asset Obtained in Exchange for Operating Lease Liability Finance leases Right-of-Use Asset Obtained in Exchange for Finance Lease Liability Consolidation And Interim Financial Information Consolidation And Interim Financial Information, Policy [Policy Text Block] Consolidation And Interim Financial Information, Policy [Policy Text Block] Use of Estimates Use of Estimates, Policy [Policy Text Block] Cash and Cash Equivalents Cash and Cash Equivalents, Policy [Policy Text Block] Revenue Recognition Revenue from Contract with Customer [Policy Text Block] Leases Lessee, Leases [Policy Text Block] Concentrations of Credit Risk Concentration Risk, Credit Risk, Policy [Policy Text Block] Income Taxes Income Tax, Policy [Policy Text Block] Recent Accounting Pronouncements New Accounting Pronouncements, Policy [Policy Text Block] Amortized Cost Debt Securities, Available-for-sale, Amortized Cost, Fiscal Year Maturity [Abstract] Due in one year or less Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, within One Year, Amortized Cost Due after one year through five years Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, after One Through Five Years, Amortized Cost Due after five years through ten years Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, after Five Through Ten Years, Amortized Cost Due after ten years Debt Securities, Available-for-sale, Allocated and Single Maturity Date, Maturity, after 10 Years, Amortized Cost Estimated Fair Value Debt Securities, Available-for-sale, Fair Value, Fiscal Year Maturity [Abstract] Due in one year or less Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, within One Year, Fair Value Due after one year through five years Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, after One Through Five Years, Fair Value Due after five years through ten years Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, after Five Through Ten Years, Fair Value Due after ten years Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, after 10 Years, Fair Value Estimated Fair Value Debt Securities, Available-for-sale, Maturity, without Single Maturity Date, Fair Value Geographical [Axis] Geographical [Axis] Geographical [Domain] Geographical [Domain] Select Health Plans California, Illinois, New Mexico, Ohio, South Carolina, Texas, Washington, and Wisconsin [Member] California, Illinois, New Mexico, Ohio, South Carolina, Texas, Washington, and Wisconsin [Member] Percentage of additional incremental revenue earned Percentage Of Additional Incremental Revenue Earned Percentage of additional incremental revenue earned. Maximum available quality incentive premium - current period Maximum Available Quality Incentive Premium Current Year Maximum available quality incentive premium current year. Quality incentive premium revenue recognized in current period: Quality Incentive Premium Revenue Recognized [Abstract] Quality Incentive Premium Revenue Recognized [Abstract] Earned current period Amount Of Current Year Quality Incentive Premium Revenue Recognized Amount of current year quality incentive premium revenue recognized. Earned prior periods Amount Of Quality Incentive Premium Revenue Recognized From Prior Year Amount of quality incentive premium revenue recognized from prior year. Total Quality Incentive Premium Revenue Recognized Quality incentive premium revenue recognized. Quality incentive premium revenue recognized as a percentage of total premium revenue Quality Incentive Premium Revenue As A Percentage Of Total Revenue Quality Incentive Premium Revenue As A Percentage Of Total Revenue Operating activities: Adjustments to reconcile net income to net cash provided by operating activities: Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Depreciation and amortization Depreciation, Depletion and Amortization Deferred income taxes Increase (Decrease) in Deferred Income Taxes Non-cash restructuring costs Non-cash Restructuring Charges Non-cash Restructuring Charges Amortization of convertible senior notes and finance lease liabilities Amortization Of Debt Discount (Premium) And Sale Leaseback Financing Obligation Amortization of Debt Discount (Premium) and Sale Leaseback Financing Obligation (Gain) loss on debt extinguishment Other, net Other Operating Activities, Cash Flow Statement Changes in operating assets and liabilities: Increase (Decrease) in Operating Capital [Abstract] Receivables Increase (Decrease) in Receivables Prepaid expenses and other current assets Increase (Decrease) in Prepaid Expense and Other Assets Medical claims and benefits payable Increase (Decrease) in Health Care Insurance Liabilities Amounts due government agencies Increase (Decrease) In Medical Premium Liability Due To Agency Increase (Decrease) in Medical Premium Liability Due to Agency Accounts payable and accrued liabilities Increase (Decrease) in Accounts Payable and Accrued Liabilities Deferred revenue Increase (Decrease) in Contract with Customer, Liability Income taxes Increase (Decrease) in Income Taxes Payable Net cash provided by operating activities Net Cash Provided by (Used in) Operating Activities Investing activities: Net Cash Provided by (Used in) Investing Activities [Abstract] Purchases of investments Payments to Acquire Marketable Securities Proceeds from sales and maturities of investments Proceeds from Sale and Maturity of Marketable Securities Purchases of property, equipment and capitalized software Payments to Acquire Property, Plant, and Equipment Other, net Payments for (Proceeds from) Other Investing Activities Net cash provided by investing activities Net Cash Provided by (Used in) Investing Activities Financing activities: Repayment of principal amount of 1.125% Convertible Notes Payments to Acquire Notes Receivable Cash paid for partial settlement of 1.125% Conversion Option Cash Paid For Settlement Of Conversion Option Cash Paid For Settlement Of Conversion Option Cash paid for partial termination of 1.125% Warrants Other, net Proceeds from (Payments for) Other Financing Activities Net cash used in financing activities Net Cash Provided by (Used in) Financing Activities Net increase 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 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 Supplemental cash flow information: Supplemental Cash Flow Information [Abstract] Schedule of non-cash investing and financing activities: Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract] Common stock used for share-based compensation Stock Issued Details of change in fair value of derivatives, net: Details of change in fair value of derivatives [Abstract] Details of change in fair value of derivatives Change in fair value of derivatives, net Derivative, Gain (Loss) on Derivative, Net 1.625% Convertible Notes exchange transaction: Business Combination, Description [Abstract] Common stock issued in exchange for 1.625% Convertible Notes Notes Issued Component allocated to additional paid-in capital, net of income taxes Notes Issued, Fair Value Adjustment Increase (Decrease) Notes Issued, Fair Value Adjustment Increase (Decrease) Net increase to additional paid-in capital Operating lease cost Operating Lease, Cost Finance lease cost: Finance Lease, Cost [Abstract] Amortization of ROU assets Finance Lease, Right-of-Use Asset, Amortization Interest on lease liabilities Finance Lease, Interest Expense Total finance lease cost Finance Lease, Cost Finance Lease, Cost Derivatives Derivative Instruments and Hedging Activities Disclosure [Text Block] Schedule of Segment Reporting Information, by Segment Schedule of Segment Reporting Information, by Segment [Table] Consolidation Items [Axis] Consolidation Items [Axis] Consolidation Items [Domain] Consolidation Items [Domain] Operating Segments Operating Segments [Member] Other operating Segment Reconciling Items [Member] Health Plans Health Plans [Member] Health plans. Other Segment Reporting Information [Line Items] Segment Reporting Information [Line Items] Gross margin Gross Profit Add: other operating revenues Less: other operating expenses Other expenses, net Commitments and Contingencies Disclosure [Abstract] Commitments and Contingencies Commitments and Contingencies Disclosure [Text Block] Basis Of Presentation [Table] Basis Of Presentation [Table] Basis Of Presentation [Table] Basis Of Presentation [Line Items] Basis Of Presentation [Line Items] Basis Of Presentation [Line Items] Number of states in which entity operates (in state) Number of States in which Entity Operates Number of members eligible for the health care programs, approximately (in member) Number Of Members Eligible For The Health Care Programs Number of members eligible for the health care programs. Minimum contract terms Minimum Contract Term Minimum contract term. Maximum contract terms Maximum Contract Term Maximum contract term. Schedule of liability for unpaid claims and claims adjustment expense Schedule of Liability for Unpaid Claims and Claims Adjustment Expense [Table Text Block] Components of change in medical claims and benefits payable Components Of Change In Medical Claims And Benefits Payable [Table Text Block] Components Of Change In Medical Claims And Benefits Payable [Table Text Block] Restricted share activity Schedule of Nonvested Restricted Stock Units Activity [Table Text Block]