Servicing Rights (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Transfers and Servicing [Abstract]
Serviced unpaid principal balance	$ 259.2		$ 259.2		$ 345.9
Unpaid principal balance for loans sold during period	77.2	$ 143.2	197.3	$ 235.2
Servicing revenue	$ 0.1	$ 0.9	$ 0.5	$ 1.4

Servicing Assets and Servicing Liabilities at Fair Value, Assumptions Used to Estimate Fair Value, Loans Sold During Period, Unpaid Principal Balance

No definition available.

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