Document and Entity Information	9 Months Ended
	Sep. 30, 2012	Oct. 31, 2012 Class A Common Stock	Oct. 31, 2012 Class B Common Stock
Entity Registrant Name	CENTURY BANCORP INC
Entity Central Index Key	0000812348
Document Type	10-Q
Document Period End Date	Sep. 30, 2012
Amendment Flag	false
Document Fiscal Year Focus	2012
Document Fiscal Period Focus	Q3
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		3,562,929	1,986,880