Document and Entity Information	9 Months Ended
	Sep. 30, 2013	Nov. 04, 2013
Document and Entity Information
Entity Registrant Name	CommonWealth REIT
Entity Central Index Key	0000803649
Document Type	10-Q
Document Period End Date	Sep. 30, 2013
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		118,387,518
Document Fiscal Year Focus	2013
Document Fiscal Period Focus	Q3