Document and Entity Information	9 Months Ended
Sep. 30, 2011	Nov. 02, 2011
Document and Entity Information
Entity Registrant Name	CommonWealth REIT
Entity Central Index Key	0000803649
Document Type	10-Q
Document Period End Date	Sep. 30, 2011
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	2011
Document Fiscal Period Focus	Q3

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End date of current fiscal year in the format --MM-DD.

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The type of document being provided (such as 10-K, 10-Q, N-1A, etc). The document type is limited to the same value as the supporting SEC submission type, minus any "/A" suffix. The acceptable values are as follows: S-1, S-3, S-4, S-11, F-1, F-3, F-4, F-9, F-10, 6-K, 8-K, 10, 10-K, 10-Q, 20-F, 40-F, N-1A, 485BPOS, 497, NCSR, N-CSR, N-CSRS, N-Q, 10-KT, 10-QT, 20-FT, and Other.

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