Summary of Discontinued Operations (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Rental revenues	$ 109,617	$ 95,742
Other revenues	9,745	8,980
Total operating revenues	119,631	104,945
Property operating expenses	80,485	71,545
Interest expense	14,350	13,914
(Loss) income from discontinued operations before gain on sale	(158)	521
Discontinued Operation, Asset Impairment	71	0
Net loss on insurance and other settlement proceeds on discontinued operations	(54)	(7)
Gain on sale of discontinued operations	9,500	0
Income from discontinued operations	9,217	514
Discontinued Operation
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Rental revenues	290	2,143
Other revenues	12	254
Total operating revenues	302	2,397
Property operating expenses	306	1,272
Depreciation and amortization	135	525
Interest expense	19	79
Total expense	$ 460	$ 1,876