CONDENSED CONSOLIDATED BALANCE SHEETS (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Real estate properties:
Land	$ 1,514,341	$ 1,450,154
Buildings and improvements	6,127,544	5,794,078
Total real estate properties, at cost, gross	7,641,885	7,244,232
Accumulated depreciation	(1,005,517)	(934,170)
Total real estate properties, at cost, net	6,636,368	6,310,062
Acquired real estate leases, net	364,282	343,917
Equity investments	180,237	177,477
Cash and cash equivalents	138,805	192,763
Restricted cash	14,329	7,869
Rents receivable, net of allowance for doubtful accounts of $12,427 and $12,575, respectively	236,001	217,592
Other assets, net	228,562	197,346
Total assets	7,798,584	7,447,026
LIABILITIES AND SHAREHOLDERS' EQUITY
Revolving credit facility		100,000
SIR revolving credit facility	321,000
Senior unsecured debt, net	2,695,152	2,845,030
Mortgage notes payable, net	801,709	632,301
Accounts payable and accrued expenses	158,044	158,272
Assumed real estate lease obligations, net	69,237	70,179
Rent collected in advance	32,163	37,653
Security deposits	24,489	23,779
Due to related persons	14,664	11,295
Total liabilities	4,116,458	3,878,509
Common shares of beneficial interest, $0.01 par value:
Common shares of beneficial interest, $0.01 par value: 350,000,000 shares authorized; 83,730,451 and 83,721,736 shares issued and outstanding, respectively	837	837
Additional paid in capital	3,590,410	3,614,079
Cumulative net income	2,522,066	2,482,321
Cumulative other comprehensive loss	(6,073)	(4,709)
Cumulative common distributions	(2,909,752)	(2,826,030)
Cumulative preferred distributions	(504,123)	(476,657)
Total shareholders' equity attributable to CommonWealth REIT	3,472,041	3,568,517
Noncontrolling interest	210,085
Total shareholders' equity	3,682,126	3,568,517
Total liabilities and shareholders' equity	7,798,584	7,447,026
Series C
50,000,000 shares authorized;
Preferred shares of beneficial interest, $0.01 par value:	145,015	145,015
Series D
50,000,000 shares authorized;
Preferred shares of beneficial interest, $0.01 par value:	368,270	368,270
Series E
50,000,000 shares authorized;
Preferred shares of beneficial interest, $0.01 par value:	$ 265,391	$ 265,391