Loans, Allowance for Loan Losses and Loans Held for Sale (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Receivables [Abstract]
Purchased loans	$ 54.6	$ 34.0
Proceeds from sale of previously charged-off loans	1.5ondk_ProceedsfromRecoveryofBadDebts	0.3ondk_ProceedsfromRecoveryofBadDebts
Allowance for loan losses for non-delinquent loans	22.5		20.5
Allowance for loan losses for delinquent loans	$ 34.3		$ 29.3

Amount of allowance to cover probable credit losses on current loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations.

No definition available.

+ Details

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

- Definition

Amount of allowance to cover probable credit losses on past due loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations.

+ References

No definition available.

+ Details

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

- Definition

The cash inflow from loans sold that were previously deemed uncollectible.

+ References

No definition available.

+ Details

Name:	ondk_ProceedsfromRecoveryofBadDebts
Namespace Prefix:	ondk_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The cash outflow associated with purchasing loans held for investment purposes during the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 13

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=56944662&loc=d3e3213-108585

+ Details

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

- Details

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