Summary of Significant Accounting Policies (Notes Receivable) (Details) (USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2012	Dec. 31, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Notes receivable	$ 17,991,000	$ 18,186,000
Number of properties sold	2
Gross deferred gain on sale of properties	12,900,000
Purchase money mortgage loan repayments terms	start in 2013, to be fully paid in 2015
20 Year Amortization Period [Member] | Purchase money mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Notes receivable	7,200,000	7,200,000
Interest rate	8.50%	8.50%
Notes receivable amortization period, years	20 years	20 years
Due 2015 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Notes receivable	300,000	500,000
Interest rate	10.00%	10.00%
Due 2016 [Member] | Purchase money mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Notes receivable	23,500,000	23,400,000
Notes receivable amortization period, years	7 years	7 years
Cash pay interest rate	6.00%	6.00%
Interest accrual rate	7.64%	7.64%
Trenton Properties [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of properties sold	2
Gross deferred gain on sale of properties	12,900,000
Expected proceeds from collection of notes receivable	$ 27,800,000