| Document and Entity Information | Sep. 08, 2020 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Sep. 8, 2020 |
| Entity Registrant Name | BERKSHIRE HILLS BANCORP INC |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 001-15781 |
| Entity Tax Identification Number | 04-3510455 |
| Entity Address, Address Line One | 60 STATE STREET |
| Entity Address, Address Line Two | 38TH FLOOR |
| Entity Address, City or Town | BOSTON |
| Entity Address, State or Province | MA |
| Entity Address, Postal Zip Code | 02109 |
| City Area Code | 617 |
| Local Phone Number | 807-8190 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| Entity Central Index Key | 0001108134 |
| Title of 12(b) Security | Common stock, par value $0.01 per share |
| Trading Symbol | BHLB |
| Security Exchange Name | NYSE |
