DOCUMENT AND ENTITY INFORMATION - USD ($)	12 Months Ended
	Dec. 31, 2020	Jan. 31, 2021
Cover [Abstract]
Entity Central Index Key	0000737468
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Amendment Flag	false
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2020
Document Transition Report	false
Entity File Number	001-32991
Entity Registrant Name	WASHINGTON TRUST BANCORP, INC
Entity Incorporation, State or Country Code	RI
Entity Tax Identification Number	05-0404671
Entity Address, Address Line One	23 Broad Street,
Entity Address, City or Town	Westerly,
Entity Address, State or Province	RI
Entity Address, Postal Zip Code	02891
City Area Code	401
Local Phone Number	348-1200
Title of 12(b) Security	COMMON STOCK, $.0625 PAR VALUE PER SHARE
Trading Symbol	WASH
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
Entity Shell Company	false
Entity Public Float	$ 553,933,925
Entity Common Stock, Shares Outstanding		17,265,339
Documents Incorporated by Reference [Text Block]	Portions of the Registrant’s Proxy Statement dated March 16, 2021 for the Annual Meeting of Shareholders to be held on April 27, 2021 are incorporated by reference into Part III of this Form 10-K.
ICFR Auditor Attestation Flag	true