Debt (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Weighted Average Interest Rate at June 30, 2019	4.60%
Total	$ 841,602	$ 816,231
OnDeck Asset Securitization Trust II | Secured Debt
Debt Instrument [Line Items]
Weighted Average Interest Rate at June 30, 2019	3.80%
Debt	$ 225,000	225,000
OnDeck Account Receivables Trust 2013-1 | Revolving Credit Facility
Debt Instrument [Line Items]
Weighted Average Interest Rate at June 30, 2019	4.20%
Debt	$ 111,827	117,664
Receivable Assets of OnDeck, LLC | Revolving Credit Facility
Debt Instrument [Line Items]
Weighted Average Interest Rate at June 30, 2019	4.80%
Debt	$ 101,453	113,631
OnDeck Asset Funding II LLC | Revolving Credit Facility
Debt Instrument [Line Items]
Weighted Average Interest Rate at June 30, 2019	5.40%
Debt	$ 110,202	109,568
Prime OnDeck Receivable Trust II | Revolving Credit Facility
Debt Instrument [Line Items]
Weighted Average Interest Rate at June 30, 2019	4.40%
Debt	$ 108,949	108,816
Loan Assets of OnDeck, LLC | Revolving Credit Facility
Debt Instrument [Line Items]
Weighted Average Interest Rate at June 30, 2019	4.20%
Debt	$ 98,469	100,000
Corporate Debt | Revolving Credit Facility
Debt Instrument [Line Items]
Weighted Average Interest Rate at June 30, 2019	5.40%
Debt	$ 20,000	0
Other Agreements
Debt Instrument [Line Items]
Weighted Average Interest Rate at June 30, 2019	6.80%
Debt	$ 72,909	47,318
Debt
Debt Instrument [Line Items]
Debt	848,809	821,997
Deferred debt issuance cost	(7,207)	(5,766)
Total	$ 841,602	$ 816,231