Changes in Accumulated Depreciation Including Real Estate Assets 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	$ 93,430	[1],[2]	$ 68,662	[1],[2]	$ 51,638
Depreciation	31,026		29,523	[2]	22,664
Depreciation on disposed property	(10,057)		(4,755)	[2]	(5,640)
Balance at end of period	$ 114,399		$ 93,430	[1],[2]	$ 68,662	[1],[2]

[1] Includes accumulated depreciation in real estate held for sale of $8,964 and $10,910 for 2011 and 2010, respectively. Excludes accumulated amortization related to intangible lease assets that are included in real estate held for sale of $1,585 and $1,941 for 2011 and 2010, respectively.

[2] 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.