Cover Page - USD ($)	12 Months Ended
	Dec. 31, 2019	Feb. 29, 2020	Jun. 30, 2019
Document Information [Line Items]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Current Fiscal Year End Date	--12-31
Entity Interactive Data Current	Yes
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Trading Symbol	CNBKA
Entity Central Index Key	0000812348
Entity Registrant Name	CENTURY BANCORP INC
Entity Public Float			$ 319,749,083
Entity Shell Company	false
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Address, State or Province	MA
Title of 12(b) Security	Class A Common Stock
Security Exchange Name	NASDAQ
Class A Common Stock [Member]
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		3,652,349
Class B Common Stock [Member]
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		1,915,560