Summary of Significant Accounting Policies (Notes Receivable) (Details) (USD $)	12 Months Ended				12 Months Ended							0 Months Ended
	Dec. 31, 2011 Properties	Dec. 31, 2010 Properties	Dec. 31, 2009 Properties	Dec. 29, 2010 Note_Receivable_Forclosed	Dec. 31, 2011 20 Year Amortization Period [Member] Purchase money mortgage [Member]	Dec. 31, 2010 20 Year Amortization Period [Member] Purchase money mortgage [Member]	Dec. 31, 2011 Due 2015 [Member]	Dec. 31, 2010 Due 2015 [Member]	Dec. 31, 2011 Due 2016 [Member] Purchase money mortgage [Member]	Dec. 31, 2010 Due 2016 [Member] Purchase money mortgage [Member]	Dec. 31, 2011 Trenton Properties [Member] Properties	Dec. 29, 2010 Gibbsboro, New Jersey [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Notes receivable	$ 18,186,000	$ 18,205,000			$ 7,200,000	$ 7,400,000	$ 500,000	$ 800,000	$ 23,400,000	$ 22,900,000	$ 23,400,000
Interest rate					8.50%	8.50%	10.00%	10.00%
Notes receivable amortization period, years					20 years	20 years			7 years	7 years
Cash pay interest rate									6.00%	6.00%
Interest accrual rate									7.64%	7.64%
Number of properties sold	19	19	19								2
Gross deferred gain on sale of properties											12,900,000
Expected proceeds from collection of notes receivable											27,800,000
Purchase money mortgage loan repayments terms	start in 2012, to be fully paid in 2014
Number of foreclosed note receivables				1
Settlement of note receivable through foreclosure of a parcel of land	$ 0	$ 2,795,000	$ 0									$ 2,800,000