Document and Entity Information	3 Months Ended
	Mar. 31, 2019 shares
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q1
Trading Symbol	CPTP
Entity Registrant Name	CAPITAL PROPERTIES INC /RI/
Entity Central Index Key	0000202947
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding	6,599,912