Summary of Significant Accounting Policies (Notes Receivable) (Details) (USD $)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011 Properties
Accounts, Notes, Loans and Financing Receivable [Line Items]
Notes receivable	$ 7,226,000		$ 7,226,000		$ 18,186,000
Number of properties sold					2
Gross deferred gain on sale of properties					12,900,000
Investment Income, Interest	311,000	523,000	2,635,000	1,385,000
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		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		12,900,000
Investment Income, Interest			$ 1,000,000