| Cover | Oct. 22, 2020 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Oct. 22, 2020 |
| Entity File Number | 000-19065 |
| Entity Registrant Name | SANDY SPRING BANCORP, INC. |
| Entity Central Index Key | 0000824410 |
| Entity Tax Identification Number | 52-1532952 |
| Entity Incorporation, State or Country Code | MD |
| Entity Address, Address Line One | 17801 Georgia Avenue |
| Entity Address, City or Town | Olney |
| Entity Address, State or Province | MD |
| Entity Address, Postal Zip Code | 20832 |
| City Area Code | 301 |
| Local Phone Number | 774-6400 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, par value $1.00 per share |
| Trading Symbol | SASR |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
