Summary of Discontinued Operations (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Rental revenues	$ 123,204	$ 108,959	$ 243,008	$ 212,518
Other Real Estate Revenue	10,766	9,840	21,029	19,319
Total operating revenues	134,112	119,008	264,356	232,315
Operating Costs and Expenses	86,482	78,970	170,555	154,930
Interest expense	15,271	14,073	30,906	28,058
(Loss) income from discontinued operations before gain on sale	907	1,293	1,812	2,535
Net loss on insurance and other settlement proceeds on discontinued operations	(4)	(2)	(4)	(56)
Gain on sale of discontinued operations	43,121	12,953	43,121	22,382
Income from discontinued operations	44,024	14,244	44,929	24,861
Disposal Groups, Including Discontinued Operations, Name [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Rental revenues	2,452	5,893	5,359	12,241
Other Real Estate Revenue	170	566	385	1,184
Total operating revenues	2,622	6,459	5,744	13,425
Operating Costs and Expenses	1,176	3,157	2,555	6,702
Depreciation	466	1,679	1,223	3,474
Interest expense	73	330	154	714
Total expense	$ 1,715	$ 5,166	$ 3,932	$ 10,890