Debt (Details) - USD ($)	Sep. 30, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Weighted Average Interest Rate at September 30, 2019	4.30%
Total	$ 870,625,000	$ 816,231,000
OnDeck Asset Securitization Trust II | Secured Debt
Debt Instrument [Line Items]
Weighted Average Interest Rate at September 30, 2019	3.80%
Debt	$ 225,000,000	225,000,000
OnDeck Account Receivables Trust 2013-1 | Revolving Credit Facility
Debt Instrument [Line Items]
Weighted Average Interest Rate at September 30, 2019	3.90%
Debt	$ 115,353,000	117,664,000
Receivable Assets of OnDeck, LLC | Revolving Credit Facility
Debt Instrument [Line Items]
Weighted Average Interest Rate at September 30, 2019	4.40%
Debt	$ 103,432,000	113,631,000
OnDeck Asset Funding II LLC | Revolving Credit Facility
Debt Instrument [Line Items]
Weighted Average Interest Rate at September 30, 2019	5.10%
Debt	$ 113,391,000	109,568,000
Prime OnDeck Receivable Trust II | Revolving Credit Facility
Debt Instrument [Line Items]
Weighted Average Interest Rate at September 30, 2019	4.00%
Debt	$ 112,593,000	108,816,000
Loan Assets of OnDeck, LLC | Revolving Credit Facility
Debt Instrument [Line Items]
Weighted Average Interest Rate at September 30, 2019	3.90%
Debt	$ 115,981,000	100,000,000
Corporate Debt | Revolving Credit Facility
Debt Instrument [Line Items]
Weighted Average Interest Rate at September 30, 2019	5.10%
Debt	$ 20,000,000	0
Other Agreements
Debt Instrument [Line Items]
Weighted Average Interest Rate at September 30, 2019	6.50%
Debt	$ 71,796,000	47,318,000
Debt
Debt Instrument [Line Items]
Debt	877,546,000	821,997,000
Deferred debt issuance cost	(6,921,000)	(5,766,000)
Total	$ 870,625,000	$ 816,231,000