Schedule III - Changes in Accumulated Depreciation Including Real Estate Assets Held for Sale (Parenthetical) (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Real Estate And Accumulated Depreciation Disclosure [Abstract]
Real estate held for sale		$ 96,766
Intangible lease assets held for sale		3,012
Accumulated depreciation of real estate held for sale		11,807
Accumulated amortization of intangible lease assets		1,949
Real estate cost included in real estate held for sale	28,617
Excludes intangible lease assets that are included in real estate held for sale	858
Includes in accumulated depreciation in real estate held for sale	3,511
Excludes accumulated amortization related to intangible lease assets that are included in real estate held for sale	426
Aggregate cost for federal income tax purposes	$ 2,155,240