Document and Entity Information	3 Months Ended
	Mar. 31, 2012	May 03, 2012
Document and Entity Information
Entity Registrant Name	CommonWealth REIT
Entity Central Index Key	0000803649
Document Type	10-Q
Document Period End Date	Mar. 31, 2012
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		83,721,736
Document Fiscal Year Focus	2012
Document Fiscal Period Focus	Q1