Summary of Significant Accounting Policies (Notes Receivable) (Details) (USD $)	6 Months Ended	12 Months Ended
	Jun. 30, 2012	Dec. 31, 2011 Properties
Accounts, Notes, Loans and Financing Receivable [Line Items]
Notes receivable	$ 7,226,000	$ 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		500,000
Interest rate	10.00%	10.00%
Proceeds from Collection of Notes Receivable	300,000
Due 2016 [Member] | Purchase money mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Notes receivable		23,400,000
Notes receivable amortization period, years	7 years	7 years
Cash pay interest rate		6.00%
Interest accrual rate		7.64%
Proceeds from Collection of Notes Receivable	23,500,000
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