CONDENSED CONSOLIDATED STATEMENTS OF INCOME (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Rental income	$ 251,246	$ 210,673
Expenses:
Operating expenses	104,090	90,397
Depreciation and amortization	61,351	52,289
General and administrative	12,310	10,959
Acquisition related costs	2,502	2,559
Total expenses	180,253	156,204
Operating income	70,993	54,469
Interest and other income	288	708
Interest expense (including net amortization of debt discounts, premiums and deferred financing fees of $746 and $2,032, respectively)	(49,106)	(47,414)
Loss on early extinguishment of debt	(67)
Equity in earnings of investees	2,958	2,712
Income from continuing operations before income tax expense	25,066	10,475
Income tax expense	(492)	(346)
Income from continuing operations	24,574	10,129
Discontinued operations:
Income from discontinued operations		1,911
Net gain on sale of properties from discontinued operations		34,572
Net income	24,574	46,612
Net income attributable to noncontrolling interest	(894)
Net income attributable to CommonWealth REIT	23,680	46,612
Preferred distributions	(13,823)	(8,839)
Net income available for CommonWealth REIT common shareholders	9,857	37,773
Amounts attributable to CommonWealth REIT common shareholders:
Income from continuing operations	9,857	1,290
Income from discontinued operations		1,911
Net gain on sale of properties from discontinued operations		34,572
Net income available for CommonWealth REIT common shareholders	$ 9,857	$ 37,773
Weighted average common shares outstanding - basic (in shares)	83,722	72,139
Weighted average common shares outstanding - diluted (in shares)	91,020	79,437
Basic and diluted earnings per common share attributable to CommonWealth REIT common shareholders:
Income from continuing operations (in dollars per share)	$ 0.12	$ 0.02
Income from discontinued operations (in dollars per share)		$ 0.51
Net income available for common shareholders (in dollars per share)	$ 0.12	$ 0.52