Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2022	Jul. 29, 2022
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2022
Document Fiscal Year Focus	2022
Document Fiscal Period Focus	Q2
Trading Symbol	CATC
Entity Registrant Name	CAMBRIDGE BANCORP
Entity Central Index Key	0000711772
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		7,006,525
Document Quarterly Report	true
Document Transition Report	false
Entity Interactive Data Current	Yes
Entity Tax Identification Number	04-2777442
Entity Current Reporting Status	Yes
Entity Shell Company	false
Entity Incorporation, State or Country Code	MA
Entity Address, Address Line One	1336 Massachusetts Avenue
Entity Address, State or Province	MA
Entity Address, City or Town	Cambridge
Entity Address, Postal Zip Code	02138
City Area Code	617
Local Phone Number	876-5500
Title of 12(b) Security	Common Stock
Security Exchange Name	NASDAQ
Entity File Number	001-38184