| Document and Entity Information | Nov. 06, 2020 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Nov. 6, 2020 |
| Entity Registrant Name | SPRING BANK PHARMACEUTICALS, INC. |
| Entity Central Index Key | 0001566373 |
| Entity Emerging Growth Company | true |
| Entity Ex Transition Period | true |
| Entity File Number | 001-37718 |
| Entity Incorporation, State or Country Code | DE |
| Entity Tax Identification Number | 52-2386345 |
| Entity Address, Address Line One | 35 Parkwood Drive |
| Entity Address, Address Line Two | Suite 210 |
| Entity Address, City or Town | Hopkinton |
| Entity Address, State or Province | MA |
| Entity Address, Postal Zip Code | 01748 |
| City Area Code | 508 |
| Local Phone Number | 473-5993 |
| Written Communications | true |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, $0.0001 par value |
| Trading Symbol | SBPH |
| Security Exchange Name | NASDAQ |
