Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2020	Jul. 31, 2020
Cover [Abstract]
Entity Registrant Name	TRUSTCO BANK CORP NY
Entity Central Index Key	0000357301
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Shell Company	false
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		96,432,657
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q2
Document Quarterly Report	true
Document Transition Report	false
Entity File Number	0-10592
Entity Tax Identification Number	14-1630287
Entity Incorporation, State or Country Code	NY
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