Changes in Total Real Estate Assets Including Real Estate Held for Sale (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Real Estate and Accumulated Depreciation [Line Items]
Balance at beginning of period	$ 1,191,096	[1]	$ 990,635	[1]	$ 934,601
Acquisitions	9,460		240,474		146,854
Transfers from construction in progress	37,174
Additions	19,971		1,011		1,709
Dispositions	(68,149)		(40,460)		(92,529)
Other			(564)
Balance at end of period	$ 1,189,552	[2]	$ 1,191,096	[1]	$ 990,635	[1]

[1] Includes real estate cost included in real estate held for sale of $68,148 and $109,173 at December 31, 2011 and 2010, respectively. Excludes intangible lease assets that are included in real estate held for sale of $2,194 and $3,555 for 2011 and 2010, respectively.

[2] The aggregate cost for federal income tax purposes is $1,183,464.