| Document and Entity Information | Mar. 29, 2024 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Mar. 29, 2024 |
| Entity File Number | 0-10592 |
| Entity Registrant Name | TrustCo Bank Corp NY |
| Entity Central Index Key | 0000357301 |
| Entity Incorporation, State or Country Code | NY |
| Entity Tax Identification Number | 14-1630287 |
| Entity Address, Address Line One | 5 SARNOWSKI DRIVE |
| Entity Address, City or Town | GLENVILLE |
| Entity Address, State or Province | NY |
| Entity Address, Postal Zip Code | 12302 |
| City Area Code | 518 |
| Local Phone Number | 377-3311 |
| Title of 12(b) Security | Common Stock, $1.00 par value |
| Trading Symbol | TRST |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
