CONSOLIDATED STATEMENTS OF OPERATIONS (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
CONSOLIDATED STATEMENTS OF OPERATIONS
Rental income	$ 1,013,092	$ 874,232	$ 720,747
Expenses:
Operating expenses	419,681	363,464	302,901
Depreciation and amortization	245,729	206,697	187,680
General and administrative	51,697	43,682	36,672
Loss on asset impairment		3,036	29,949
Acquisition related costs	5,648	10,073	21,553
Total expenses	722,755	626,952	578,755
Operating income	290,337	247,280	141,992
Interest and other income	1,428	1,662	2,171
Interest expense (including net amortization of debt discounts, premiums and deferred financing fees of $3,405, $6,943 and $7,150, respectively)	(204,244)	(195,024)	(179,642)
Loss on early extinguishment of debt	(1,895)	(35)	(796)
Equity in earnings of investees	11,420	11,377	8,464
Gain on issuance of shares by an equity investee	7,246	11,177	34,808
Gain on asset acquisition			20,392
Income from continuing operations before income tax expense	104,292	76,437	27,389
Income tax expense	(3,207)	(1,347)	(550)
Income from continuing operations	101,085	75,090	26,839
Discontinued operations:
(Loss) income from discontinued operations	(14,337)	(539)	36,029
Loss on asset impairment from discontinued operations	(168,632)	(7,319)	(99,315)
Loss on early extinguishment of debt from discontinued operations			(248)
Net gain on sale of properties from discontinued operations	2,039	42,752	137,768
(Loss) income before gain on sale of properties	(79,845)	109,984	101,073
Gain on sale of properties			34,336
Net (loss) income	(79,845)	109,984	135,409
Net income attributable to noncontrolling interest in consolidated subsidiary	(15,576)
Net (loss) income attributable to CommonWealth REIT	(95,421)	109,984	135,409
Preferred distributions	(51,552)	(46,985)	(47,733)
Excess redemption price paid over carrying value of preferred shares	(4,985)		(5,921)
Net (loss) income available for CommonWealth REIT common shareholders	(151,958)	62,999	81,755
Amounts attributable to CommonWealth REIT common shareholders:
Income from continuing operations	28,972	28,105	7,521
(Loss) income from discontinued operations	(14,337)	(539)	36,029
Loss on asset impairment from discontinued operations	(168,632)	(7,319)	(99,315)
Loss on early extinguishment of debt from discontinued operations			(248)
Net gain on sale of properties from discontinued operations	2,039	42,752	137,768
Net (loss) income available for CommonWealth REIT common shareholders	$ (151,958)	$ 62,999	$ 81,755
Weighted average common shares outstanding - basic and diluted (in shares)	83,750	77,428	64,703
Basic and diluted earnings per common share attributable to CommonWealth REIT common shareholders:
Income from continuing operations (in dollars per share)	$ 0.35	$ 0.36	$ 0.12
(Loss) income from discontinued operations (in dollars per share)	$ (2.16)	$ 0.45	$ 1.15
Net (loss) income (in dollars per share)	$ (1.81)	$ 0.81	$ 1.26