Debt, Long-term and Short-term, Combined Amount, Gross

No definition available.

Name:	ondk_DebtLongtermandShorttermCombinedAmountGross
Namespace Prefix:	ondk_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Line of Credit Facility, Maximum Borrowing Capacity, Increase

+ References

No definition available.

+ Details

Name:	ondk_LineofCreditFacilityMaximumBorrowingCapacityIncrease
Namespace Prefix:	ondk_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of increase (decrease) of the credit facility.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(f))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

+ Details

Name:	us-gaap_LineOfCreditFacilityIncreaseDecreaseForPeriodNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The carrying amount as of the date of the latest financial statement presented of other securities classified as available for sale or held for investment which are owned but transferred to another party to serve as collateral to partially or fully secure a debt obligation, repurchase agreement or other current or potential obligation, and for which the transferee does not have the right by contract or custom to sell or re-pledge them to an unrelated party.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 50
-Paragraph 1A
-Subparagraph (b)(1)(i)
-URI http://asc.fasb.org/extlink&oid=109249958&loc=SL6224234-111729

+ Details

Name:	us-gaap_PledgedFinancialInstrumentsNotSeparatelyReportedOtherDebtSecuritiesAvailableForSaleOrHeldForInvestment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_DebtInstrumentAxis=ondk_CreditFacilityDueDecember2019Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_RevolvingCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=ondk_CorporateDebtMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=ondk_DebtFacilitySunTrustFacilityAgreementDueJanuary2021Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=ondk_AustralianDebtFacilityAgreementDueDecember2021Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_LondonInterbankOfferedRateLIBORMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Debt (Narrative) (Details)	Jul. 19, 2019 USD ($)	Dec. 17, 2018 USD ($)	Sep. 30, 2019 USD ($)	Jul. 02, 2019 AUD ($)	Jul. 01, 2019 AUD ($)	Dec. 31, 2018 USD ($)
Debt Instrument [Line Items]
Loans held for investment that are pledged as collateral			$ 1,100,000,000			$ 1,000,000,000
Credit Facility Due December 2019 \| Revolving Credit Facility
Debt Instrument [Line Items]
Increase in line of credit		$ 19,700,000
Corporate Debt \| Revolving Credit Facility
Debt Instrument [Line Items]
Debt, prepaid in full			$ 20,000,000			$ 0
Debt Facility Sun Trust Facility Agreement Due January 2021 \| Revolving Credit Facility
Debt Instrument [Line Items]
Line of credit facility, increase	$ 20,000,000
Line of credit facility, maximum borrowing capacity	$ 105,000,000
Australian Debt Facility Agreement Due December 2021 \| Revolving Credit Facility
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity				$ 150,000,000	$ 75,000,000
LIBOR \| Debt Facility Sun Trust Facility Agreement Due January 2021 \| Revolving Credit Facility
Debt Instrument [Line Items]
Basis spread on variable rate	3.00%