| Document and Entity Information | Oct. 07, 2020 |
| Cover [Abstract] | |
| Amendment Flag | false |
| Entity Central Index Key | 0001420811 |
| Document Type | 8-K |
| Document Period End Date | Oct. 7, 2020 |
| Entity Registrant Name | On Deck Capital, Inc. |
| Entity Incorporation State Country Code | DE |
| Entity File Number | 001-36779 |
| Entity Tax Identification Number | 42-1709682 |
| Entity Address, Address Line One | 1400 Broadway |
| Entity Address, Address Line Two | 25th Floor |
| Entity Address, City or Town | New York |
| Entity Address, State or Province | NY |
| Entity Address, Postal Zip Code | 10018 |
| City Area Code | (888) |
| Local Phone Number | 269-4246 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Security 12b Title | Common Stock, par value $0.005 per share |
| Trading Symbol | ONDK |
| Security Exchange Name | NYSE |
| Entity Emerging Growth Company | false |
