CONDENSED CONSOLIDATED BALANCE SHEETS (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Real estate properties:
Land	$ 1,531,466	$ 1,450,154
Buildings and improvements	6,331,605	5,794,078
Total real estate properties, at cost, gross	7,863,071	7,244,232
Accumulated depreciation	(1,045,477)	(934,170)
Total real estate properties, at cost, net	6,817,594	6,310,062
Acquired real estate leases, net	371,929	343,917
Equity investments	178,996	177,477
Cash and cash equivalents	72,680	192,763
Restricted cash	13,631	7,869
Rents receivable, net of allowance for doubtful accounts of $11,798 and $12,575, respectively	246,313	217,592
Other assets, net	245,812	197,346
Total assets	7,946,955	7,447,026
LIABILITIES AND SHAREHOLDERS' EQUITY
Revolving credit facility	160,000	100,000
SIR revolving credit facility	92,000
Senior unsecured debt, net	3,029,652	2,845,030
Mortgage notes payable, net	869,384	632,301
Accounts payable and accrued expenses	143,192	158,272
Assumed real estate lease obligations, net	70,587	70,179
Rent collected in advance	25,883	37,653
Security deposits	24,191	23,779
Due to related persons	31,942	11,295
Total liabilities	4,446,831	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; 83,804,068 and 83,721,736 shares issued and outstanding, respectively	838	837
Additional paid in capital	3,585,964	3,614,079
Cumulative net income	2,539,684	2,482,321
Cumulative other comprehensive loss	(1,044)	(4,709)
Cumulative common distributions	(2,951,618)	(2,826,030)
Cumulative preferred distributions	(518,215)	(476,657)
Total shareholders' equity attributable to CommonWealth REIT	3,289,270	3,568,517
Noncontrolling interest	210,854
Total shareholders' equity	3,500,124	3,568,517
Total liabilities and shareholders' equity	7,946,955	7,447,026
Series C
50,000,000 shares authorized;
Preferred shares of beneficial interest, $0.01 par value:		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