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Document and Entity Information - USD ($)
 12 Months Ended
Dec. 31, 2023
Feb. 16, 2024
Jun. 30, 2023
Cover [Abstract]      
Document Type 10-K    
Amendment Flag false    
Document Period End Date Dec. 31, 2023    
Document Fiscal Year Focus 2023    
Document Fiscal Period Focus FY    
Trading Symbol CPTP    
Entity Registrant Name CAPITAL PROPERTIES, INC.    
Entity Central Index Key 0000202947    
Current Fiscal Year End Date --12-31    
Entity Filer Category Non-accelerated Filer    
Entity Small Business true    
Entity Shell Company false    
Document Financial Statement Error Correction [Flag] false    
Entity Emerging Growth Company false    
Entity Current Reporting Status Yes    
Entity File Number 001-08499    
Entity Tax Identification Number 05-0386287    
Entity Address, Address Line One 5 Steeple Street, Unit 303    
Entity Address, City or Town Providence    
Entity Address, State or Province RI    
Entity Address, Postal Zip Code 02903    
City Area Code 401    
Local Phone Number 435-7171    
Entity Interactive Data Current Yes    
Document Annual Report true    
Document Transition Report false    
Entity Common Stock, Shares Outstanding   6,599,912  
Entity Incorporation, State or Country Code RI    
Entity Well-known Seasoned Issuer No    
Entity Voluntary Filers No    
Entity Public Float     $ 23,000
Title of 12(g) Security Class A Common Stock, $.01 par value    
Auditor Name Stowe & Degon, LLC    
Auditor Location Westborough, MA, USA    
Auditor Firm ID 577    
Documents Incorporated by Reference

DOCUMENTS INCORPORATED BY REFERENCE

Portions of the Company’s Proxy Statement for the 2024 Annual Meeting of Shareholders to be held on April 24, 2024, are incorporated by reference into Part III of this Form 10-K.