Cover Page - USD ($)	12 Months Ended
	Dec. 31, 2020	Feb. 26, 2021	Jun. 30, 2020
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2020
Current Fiscal Year End Date	--12-31
Document Transition Report	false
Entity File Number	0-12507
Entity Registrant Name	ARROW FINANCIAL CORPORATION
Entity Incorporation, State or Country Code	NY
Entity Tax Identification Number	22-2448962
Entity Address, Address Line One	250 Glen Street,
Entity Address, City or Town	Glens Falls
Entity Address, State or Province	NY
Entity Address, Postal Zip Code	12801
City Area Code	518
Local Phone Number	745-1000
Title of 12(b) Security	Common Stock, Par Value $1.00 per share
Trading Symbol	AROW
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float			$ 447,236,731
Entity Common Stock, Shares Outstanding (in shares)		15,526,490
Documents Incorporated by Reference	Portions of the Registrant’s Proxy Statement for the Annual Meeting of Stockholders to be held May 5, 2021 (Part III).
Entity Central Index Key	0000717538
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Amendment Flag	false