Document And Entity Information Note To Financial Statement Details Textual Significant Accounting Policies Note 2 - Significant Accounting Policies and Consolidated Financial Statement Components Note 3 - Segment Reporting Note 5 - Investment in Equity-method Investee Note 6 - Fair Values of Assets and Liabilities Note 7 - Notes Payable Note 8 - Convertible Senior Notes Note 10 - Net Loss Attributable to Controlling Interests Per Common Share Note 11 - Stock-based Compensation Note 2 - Significant Accounting Policies and Consolidated Financial Statement Components - Summary of Allowance for Uncollectible Loans and Fees Receivable (Details) Note 2 - Significant Accounting Policies and Consolidated Financial Statement Components - Summary of Aging of Delinquent Loans and Fees Receivable (Details) Note 2 - Significant Accounting Policies and Consolidated Financial Statement Components - Summary of Troubled Debt Restructurings (Details) Note 2 - Significant Accounting Policies and Consolidated Financial Statement Components - Summary of Fees and Related Income on Earning Assets (Details) Note 2 - Significant Accounting Policies and Consolidated Financial Statement Components - Components of Revenue from Contracts with Customers (Details) Note 3 - Segment Reporting - Summary of Operating Segment Information (Details) Schedule of Debt [Table Text Block] Credit Card Receivable [Member] Note 5 - Investment in Equity-method Investee - Summary of Equity-method Investee (Details) Note 6 - Fair Values of Assets and Liabilities - Summary of Fair Value Hierarchy for Assets (Details) Note 6 - Fair Values of Assets and Liabilities - Reconciliation of Level 3 Assets (Details) Note 6 - Fair Values of Assets and Liabilities - Quantitative Information about Level 3 Assets and Liabilities Fair Value Measurements (Details) Note 6 - Fair Values of Assets and Liabilities - Summary of Fair Value Hierarchy for Liabilities (Details) Note 6 - Fair Values of Assets and Liabilities - 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Controlling Interests Per Common Share - Summary of Earning Per Share (Details) Note 11 - Stock-based Compensation - Summary of Outstanding Options (Details) Notes To Financial Statements Notes To Financial Statements [Abstract] Reclassifications of foreign currency translation adjustment to Other operating expense on the consolidated statements of operations us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period Number of accounts on non-accrual status Financing Receivable Modifications Number Of Contracts Outstanding. us-gaap_OtherComprehensiveIncomeLossTax Income tax expense related to other comprehensive income Exercisable, weighted average exercise price (in dollars per share) Exercisable, weighted average remaining contractual life (Year) Exercisable, aggregate intrinsic value Exercisable (in shares) 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Credit Facility [Domain] us-gaap_PolicyTextBlockAbstract Accounting Policies Notes payable associated with capital leases us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant Issuance of stock options and restricted stock us-gaap_PaymentsToAcquirePropertyPlantAndEquipment Purchases and development of property, net of disposals Effect of dilutive stock compensation arrangements (2) (in shares) us-gaap_IncrementalCommonSharesAttributableToConversionOfDebtSecurities Incremental Common Shares Attributable to Conversion of Debt Securities, Total us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period us-gaap_WeightedAverageNumberOfSharesRestrictedStock Weighted Average Number of Shares, Restricted Stock 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on outstanding notes payable, net Entity Filer Category Debt Instrument [Axis] Entity Current Reporting Status Debt Instrument, Name [Domain] us-gaap_AdjustmentToAdditionalPaidInCapitalIncomeTaxEffectFromShareBasedCompensationNet Adjustment to Additional Paid in Capital, Income Tax Effect from Share-based Compensation, Net, Total us-gaap_IncreaseDecreaseInAccruedInterestReceivableNet (Increase) decrease in uncollected fees on earning assets Schedule of Long-term Debt Instruments [Table Text Block] Amortization of deferred stock-based compensation costs Statement of Comprehensive Income [Abstract] us-gaap_ServicingAsset Servicing Asset, Total Entity Central Index Key Entity Registrant Name Entity [Domain] Legal Entity [Axis] us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue Balance Balance Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block] Balance at beginning of period Balance at end of period us-gaap_FinancingReceivableAllowanceForCreditLosses us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements Settlements Entity Common Stock, Shares Outstanding (in shares) Depreciation us-gaap_StockRepurchasedAndRetiredDuringPeriodValue Stock Repurchased and Retired During Period, Value Redemption and retirement of shares Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block] us-gaap_StockRepurchasedAndRetiredDuringPeriodShares Stock Repurchased and Retired During Period, Shares Redemption and retirement of shares (in shares) Marketing and solicitation Notes payable associated with structured financings, measurement input us-gaap_LoansAndLeasesReceivableNetReportedAmount Net loans and fees receivable Loans and fees receivable, gross Loans and fees receivable, gross us-gaap_LoansAndLeasesReceivableDeferredIncome Loans and Leases Receivable, Deferred Income, Total Deferred revenue Long-term Debt [Text Block] us-gaap_LoansAndLeasesReceivableAllowance Allowances for uncollectible loans and fees receivable Trading Symbol Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block] Stock options exercises and proceeds related thereto (in shares) Exercised (in shares) us-gaap_TableTextBlock Notes Tables Revolving credit facility, maximum borrowing capacity Line of Credit Facility, Maximum Borrowing Capacity Compensatory stock issuances, net of forfeitures (in shares) Stock options exercises and proceeds related thereto Loans and fees receivable: Issued (in shares) Revolving credit facility, expiration date Line of Credit Facility, Expiration Date Line of Credit Facility, Lender [Domain] Lender Name [Axis] us-gaap_LiabilitiesAndStockholdersEquity Total liabilities and equity Retained deficit Accumulated other comprehensive loss Measurement Input, Prepayment Rate [Member] Measurement Input, Discount Rate [Member] Debt Disclosure [Text Block] us-gaap_InterestExpense Interest expense Interest expense Measurement Input, Default Rate [Member] Changes in assets and liabilities: us-gaap_DisclosureTextBlockAbstract Notes to Financial Statements Subsequent Event [Member] Subsequent Event Type [Axis] Subsequent Event Type [Domain] Proceeds from equity-method investees us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardCompensationCost1 Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost, Total Measurement Input, Constant Prepayment Rate [Member] Measurement Input Type [Axis] Measurement Input Type [Domain] Valuation Technique, Discounted Cash Flow [Member] Valuation Approach and Technique [Axis] Valuation Approach and Technique [Domain] Subsequent Events, Policy [Policy Text Block] Interest expense from accretion of discount on notes Other Other Income Tax, Policy [Policy Text Block] us-gaap_InterestAndDividendIncomeOperating Total interest income Total interest income us-gaap_AccretionAmortizationOfDiscountsAndPremiumsInvestments Income from accretion of discount associated with receivables purchases Depreciation, amortization and accretion, net Stockholders' Equity Note Disclosure [Text Block] Fair Value Measurement Inputs and Valuation Techniques [Table Text Block] Common stock, no par value, 150,000,000 shares authorized: 15,372,542 shares issued and outstanding (including 1,459,233 loaned shares to be returned) at September 30, 2018; and 15,291,884 shares issued and outstanding (including 1,459,233 loaned shares to be returned) at December 31, 2017 Measurement Frequency [Axis] Adjustments to reconcile net loss to net cash used in operating activities: us-gaap_AmortizationOfDeferredLoanOriginationFeesNet Amortization of deferred loan costs Fair Value, Measurement Frequency [Domain] Fair Value, Measurements, Recurring [Member] Common stock, authorized (in shares) Common stock, issued (in shares) Consumer loans, including past due fees Consumer loans, including past due fees Common stock, par value (in dollars per share) Range [Domain] Maximum [Member] Supplemental non-cash information Minimum [Member] Weighted Average [Member] Product and Service [Axis] Product and Service [Domain] Range [Axis] Interest income: Cash paid for interest Other Income Total other operating income Revenue from contracts with customers Servicing income Servicing income Fair Value, Inputs, Level 3 [Member] Fair Value Hierarchy and NAV [Domain] Fair Value, Inputs, Level 1 [Member] Fair Value, Inputs, Level 2 [Member] Other operating income: Fair Value Hierarchy and NAV [Axis] us-gaap_ProceedsFromIncomeTaxRefunds Proceeds from Income Tax Refunds us-gaap_InterestIncomeExpenseAfterProvisionForLoanLoss Net interest income, fees and related income on earning assets us-gaap_InterestIncomeExpenseNet Net interest income before fees and related income on earning assets and provision for losses on loans and fees receivable Noncontrolling interests Operating activities Schedule of Segment Reporting Information, by Segment [Table Text Block] Revenue Recognition, Policy [Policy Text Block] Statement [Line Items] us-gaap_NumberOfReportableSegments Number of Reportable Segments Additional paid-in capital AOCI Attributable to Parent [Member] us-gaap_OtherNonoperatingIncomeExpense Other Loans and fees receivable, at fair value Other us-gaap_NonoperatingIncomeExpense Segment Reporting Disclosure [Text Block] Equity Credit and Debit Card [Member] Fair Value Disclosures [Text Block] us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations Cash and cash equivalents at beginning of period Cash and cash equivalents at end of period Assets Net income (loss) us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect Net (decrease) increase in cash and cash equivalents us-gaap_NetCashProvidedByUsedInFinancingActivities Net cash provided by financing activities Net interest income, fees and related income (loss) on earning assets us-gaap_Liabilities Total liabilities Commitments and contingencies (Note 9) Fees and related income on earning assets Total fees and related income on earning assets Fees and related income on earning assets Fees and related income on earning assets primarily include: (1) lending fees; (2) fees associated with our credit card receivables; (3) changes in the fair value of loans and fees receivable; (4) changes in fair value of notes payable associated with structured financings; (5) income on investments in previously charged-off receivables; (6) gross profits and losses from auto sales; (7) gains associated with investments in securities; and (8) gains realized associated with our settlement of litigation. Members’ capital us-gaap_NetCashProvidedByUsedInOperatingActivities Net cash used in operating activities Notes payable associated with structured financings, at fair value Amortizing securitization facility (stated maturity of December 2021), outstanding face amount of $101.3 million as of September 30, 2018 ($101.3 million as of December 31, 2017) bearing interest at a weighted average 7.3% interest rate at September 30, 2018 (6.7% at December 31, 2017), which is secured by credit card receivables and restricted cash aggregating $6.2 million as of September 30, 2018 ($9.2 million as of December 31, 2017) in carrying amount Notes Payable Associated with Structured Financings, Fair Value Notes payable associated with structured financings, at fair value Debt that reflects the fair value of the consolidation of our securitization trusts presenting certain non-recourse, asset-backed structured financing debt facilities that are secured by these credit card receivables that are held within such trusts. us-gaap_NetCashProvidedByUsedInInvestingActivities Net cash used in investing activities Effect of exchange rate changes on cash Total liabilities Card and loan servicing (Net recovery of) losses upon charge off of loans and fees receivable recorded at fair value Net recovery of (losses upon) charge off of loans and fees receivable recorded at fair value Reflects charge offs associated with the de-securitization and reconsolidation of our lower-tier credit card receivables portfolio upon investor repayment and the consolidation of our formerly off-balance-sheet credit card receivables securitizations pursuant to accounting rules changes. Loans and fees receivables, at fair value Total assets atlc_UnrealizedGainOnLoansAndFeesReceivableAndUnderlyingNotesPayableHeldAtFairValue Unrealized gain on loans and fees receivable and underlying notes payable held at fair value The aggregate increase (decrease) in the market value on loans and fees receivable and underlying notes payable held at fair value whose gains (losses) were included in earnings. Accounts Payable and Accrued Expenses [Policy Text Block] The entire policy related to accounts payable and accrued expenses. Prepaid Expenses and Other Assets [Policy Text Block] The entire policy related to prepaid expenses and other assets. atlc_WeightedAverageRemainingAccretionPeriodOfDeferredRevenue Weighted Average Remaining Accretion Period of Deferred Revenue Represents the weighted average remaining accretion period of deferred revenue during the reporting period. Carrying value of receivables on non-accrual status (in thousands) Represents the carrying value of the outstanding recorded investment related to financing receivables that have been modified by troubled debt restructurings. Direct-to-Consumer [Member] Information related to items classified as direct-to-consumer. Point-of-Sale [Member] Information related to items classified as point-of-sale. Other Unsecured Lending Products [Member] Information related to other unsecured lending products. Accounts payable and accrued expenses Noncontrolling interests contributions, net Components of Fees and Related Income on Earning Assets [Table Text Block] Tabular disclosure of the components of fees and related income on earning assets. Income tax liability Auto Finance [Member] Information related to auto finance. Credit and Other Investments [Member] Information related to credit and other investments. Service Charges and Other Customer Related Fees [Member] Information related to service charges and other customer related fees. Servicing Income [Member] Information related to servicing income. Equity Method Investments and Joint Ventures Disclosure [Text Block] Equity Method Investments [Table Text Block] atlc_DepreciationOfLeasedMerchandise Depreciation of rental merchandise Represents the amount of depreciation of leased merchandise during the period. Noncontrolling Interest [Member] us-gaap_NoninterestExpense Total other operating expense Impact of foreign currency translation This element represents impact of foreign currency translation on assets measured at fair value on a recurring basis using unobservable inputs (Level 3) which have taken place during the period. Loans and fees receivable, net for which it is practicable to estimate fair value This item represents a financial instrument (as defined) for which it is practicable to estimate fair value. This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents loan receivable as presented on the statement of financial position which may include mortgage loans held for investment, finance receivables held for investment, policy loans on insurance contracts, or any other loans which are due the Company as of the balance sheet date. us-gaap_PaymentsForRepurchaseOfCommonStock Purchase and retirement of outstanding stock Measurement Input, Servicing Rate [Member] Measurement input represents the expected servicing rate. Measurement Input, Gross Yield [Member] Measurement input representing the gross yield. us-gaap_TaxAdjustmentsSettlementsAndUnusualProvisions Tax Adjustments, Settlements, and Unusual Provisions us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestExpense Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense, Total Loans and fees receivable, measurement input Value of input used to measure loans and fees receivable. Five Point Eight Seven Five Percent Convertible Senior Notes Due Two Thousand Thirty Five [Member] Information related to 5.875% convertible senior notes due 2035. Retained Earnings [Member] Proceeds from exercise of stock options Aggregate unpaid principal balance within loans and fees receivable that are reported at fair value This item represents the aggregate unpaid principal balance within loans and fees receivables that are reported at fair value for which the fair value option has been elected. Loans and Fees Receivable Pledged as Collateral, Fair Value [Member] Information related to loans and fees receivable pledged as collateral measured at fair value. Loans and Fees Receivable at Fair Value [Member] Information related to loans and fees receivable measure at fair value. Changes in fair value of notes payable associated with structured financings recorded at fair value Net revaluations of notes payable associated with structured financings, at fair value This element represents [net] revaluations of notes payable liability measured at fair value on a recurring basis using unobservable inputs (Level 3) which have taken place during the period. Amortizing securitization facility, amount secured by credit card receivables and restricted cash Credit Card Receivables and Restricted Cash Carrying Amount as Security for Notes Payable This line item represents aggregate carrying amount of credit card receivables and restricted cash that provides security for structured financing notes, as of balance sheet date. Other operating expense: Structured Financing Notes Payable [Member] Information related to notes payable associated with structured financing reported at fair value. Aggregate fair value of notes payable This item represents the aggregate fair value of notes payable for which the fair value option has been elected. Additional Paid-in Capital [Member] Common Stock [Member] Equity Components [Axis] Equity Component [Domain] us-gaap_IncomeTaxExaminationInterestAccrued Income Tax Examination, Interest Accrued Class of Financing Receivable, Type [Domain] us-gaap_NotesPayable Total notes payable outstanding Class of Financing Receivable, Type [Axis] Notes payable, at face value Revolving credit facilities Long-term Line of Credit, Total Loans and Leases Receivable, Troubled Debt Restructuring Policy [Policy Text Block] Other comprehensive income: Convertible senior notes Net carrying value us-gaap_DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet Unamortized debt issuance costs and discounts Amortizing debt facilities Disaggregation of Revenue [Table Text Block] us-gaap_RepaymentsOfLongTermDebt Repayment of borrowings The 2014 Plan [Member] Information related to the 2014 Equity Incentive Plan (the "2014 Plan"). Employee Stock Purchase Plan [Member] Information related to the Employee Stock Purchase Plan (the "ESPP"). Senior Secured Term Loan Facility [Member] Information related to a Senior Secured Term Loan Facility. Dove Ventures, LLC [Member] Information related to Dove Ventures, LLC, a Nevada limited liability company ("Dove"). atlc_AggregateExposureToPretaxEquityLossStructuredFinancingAtFairValue Aggregate Exposure to Pretax Equity Loss, Structured Financing at Fair Value Represents the aggregate exposure to pre-tax equity loss associated with structured financing measured at fair value. Trust Funding Notes Facility [Member] Information related to a program where the company may sell certain receivables to a consolidated trust in exchange for notes issued by the trust by an unaffiliated third party. us-gaap_DebtInstrumentUnamortizedDiscount Discount Receivables, Policy [Policy Text Block] Revolving Credit Facility Expiring October 30, 2019 [Member] Information related to a revolving credit facility expiring October 30, 2019. Accounting Policies [Abstract] Revolving Credit Facility Expiring November 1, 2019 [Member] Information related to a revolving credit facility expiring November 1, 2019. Significant Accounting Policies [Text Block] Basis of Accounting, Policy [Policy Text Block] Additional Trust Funding Notes Facility [Member] Information related to an additional program where the company may sell certain receivables to a consolidated trust in exchange for notes issued by the trust by an unaffiliated third party. Revolving Credit Facility Expiring December 31, 2019 [Member] Information related to a revolving credit facility expiring December 31, 2019. Revolving Credit Facility Expiring December 21, 2019 [Member] Information related to a revolving credit facility expiring December 21, 2019. Revolving Credit Facility Expiring September 19, 2021 [Member] Information related t a revolving credit facility expiring September 19, 2021. Revolving Credit Facility Expiring June 25, 2020 [Member] Information related t a revolving credit facility expiring June 25, 2020. Revolving Credit Facility Expiring June 11, 2020 [Member] Information related to a revolving credit facility expiring June 11, 2020. Revolving Credit Facility Expiring February 8, 2022 [Member] Information related to a revolving credit facility expiring February 8, 2022. Revolving credit facility, amount of securing assets This line item represents aggregate carrying amount of receivables and other assets that provides security for structured financing notes, as of balance sheet date. Amortizing Debt Facility Expiring September 29, 2019 [Member] Information related to an amortizing debt facility expiring September 29, 2019. Amortizing Debt Facility Expiring April 22, 2019 [Member] Information related to an amortizing debt facility expiring April 22, 2019. Amortizing Debt Facility Expiring November 30, 2018 [Member] Information related to an amortizing debt facility expiring November 30, 2018. Proceeds from borrowings Proceeds from Issuance of Long-term Debt, Total us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesExpense Unrecognized Tax Benefits, Income Tax Penalties Expense Amortizing Debt Facility [Member] Information related to an amortizing debt facility. Total notes payable before unamortized debt issuance costs and discounts The gross amount of Notes Payable. Changes in fair value of loans and fees receivable recorded at fair value Represents the increase (decrease) during the period in the fair value of loans and fees receivable. atlc_PaymentOfIncomeTaxSettlement Payment of Income Tax Settlement Represents the amount of payment related to income tax settlements includes but is not limited to unpaid income tax assessment and the accrued interest related to the settlement. Unfunded Outstanding Floor-Plan Financing Commitment [Member] Information related to unfunded outstanding floor-plan financing commitments. Unfunded Individual Credit Commitment [Member] Information related to unfunded commitments related to consumers ability to borrow up to the maximum credit limit assigned to each individual account. Fees on credit products Represents the amount of revenue related to fees on credit products. Rental revenue Amount of leased merchandise revenue and associated fees during the period. Segments [Axis] Segments [Domain] us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding Diluted (including unvested share-based payment awards) (1) (in shares) Senior secured term loan Asset Class [Axis] Asset Class [Domain] Statement [Table] Scenario [Axis] Statement of Financial Position [Abstract] Net loss attributable to controlling interests per common share—diluted (in dollars per share) Scenario, Unspecified [Domain] Amortizing Debt Facility Repaid June 2018 [Member] Information related to an amortizing debt facility repaid in June 2018. Basic (including unvested share-based payment awards) (1) (in shares) us-gaap_OperatingLeasesFutureMinimumPaymentsDue Operating Leases, Future Minimum Payments Due, Total Amortizing Debt Facility Repaid March 2018 [Member] Information related to an amortizing debt facility repaid in March 2018. us-gaap_EffectiveIncomeTaxRateContinuingOperations Effective Income Tax Rate Reconciliation, Percent, Total Net loss attributable to controlling interests per common share—basic (in dollars per share) Amortizing Debt Facility Repaid September 2018 [Member] Information related to an amortizing debt facility repaid in September 2018. Statement of Cash Flows [Abstract] Statement of Stockholders' Equity [Abstract] atlc_InterestIncomeExpenseBeforeFees Net interest income before fees and related income on earning assets and provision for losses on loans and fees receivable The net amount of operating interest income (expense) before fees. Income Statement [Abstract] Schedule of Credit Losses Related to Financing Receivables, Current and Noncurrent [Table Text Block] Provision for losses on loans and fees receivable Provision for loan losses Amount of expense for provision for losses on loans and fees receivable recorded at net realizable value. us-gaap_OtherCommitment Other Commitment, Total Other Commitments [Axis] Fair Value, Assets Measured on Recurring Basis [Table Text Block] Other Commitments [Domain] Fair Value, Liabilities Measured on Recurring Basis [Table Text Block] Financing activities 5.875% convertible senior notes Foreign currency translation adjustment us-gaap_StockholdersEquity Total shareholders’ equity Class of Stock [Axis] Schedule of Earnings Per Share, Basic and Diluted [Table Text Block]