Document And Entity Information - shares	3 Months Ended
	Mar. 31, 2026	Apr. 30, 2026
Document Information Line Items
Entity Central Index Key	0000357301
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2026
Document Fiscal Year Focus	2026
Document Transition Report	false
Entity File Number	000-10592
Entity Registrant Name	TRUSTCO BANK CORP NY
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 Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		17,474,811
Amendment Flag	false
Document Fiscal Period Focus	Q1
Current Fiscal Year End Date	--12-31