Sale of Land and Building (Detail) (USD $)	9 Months Ended
	Sep. 30, 2012 acre sqft
Property, Plant and Equipment [Line Items]
Selling price of property and other related assets	$ 180,000,000
Area of building to be sold	294,000
Selling property of land	4
Assets held for sale	62,144,000
Direct costs	1,000,000
Synthetic Lease [Member]
Property, Plant and Equipment [Line Items]
Assets held for sale	56,900,000
Land
Property, Plant and Equipment [Line Items]
Assets held for sale	2,900,000
Leasehold And Land Improvements [Member]
Property, Plant and Equipment [Line Items]
Assets held for sale	2,100,000
Synthetic Lease Capitalized Financing Cost [Member]
Property, Plant and Equipment [Line Items]
Assets held for sale	$ 200,000