Servicing Rights (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Transfers and Servicing [Abstract]
Serviced unpaid principal balance	$ 196.0		$ 222.0
Unpaid principal balance for loans sold during period	41.1	$ 120.2
Servicing revenue	$ 0.3	$ 0.4

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