Related Party Transactions and Investments in Non-Consolidated Entities (Details 3) (USD $)	3 Months Ended
	Mar. 31, 2013 entity	Mar. 31, 2012 entity	Dec. 31, 2012 entity
Related Party Transactions and Investments in Non-Consolidated Entities
Sponsored REITs (in entities)	15	16	15
Balance Sheet Data (unaudited):
Real Estate, net	$ 659,062,000	$ 659,655,000
Other assets	154,496,000	156,785,000
Total liabilities	(317,365,000)	(316,311,000)
Total stockholders' equity	496,193,000	500,129,000
Operating Data (unaudited):
Rental revenues	23,372,000	27,658,000
Other revenues	18,000	37,000
Operating and maintenance expenses	(11,588,000)	(13,750,000)
Depreciation and amortization	(7,842,000)	(8,672,000)
Interest expense	(3,307,000)	(4,381,000)
Net income	653,000	892,000
Asset management fees, low end of range (as a percent)	1.00%
Asset management fees, high end of range (as a percent)	5.00%
Notice period for cancellation of applicable contracts	30 days
Asset management fee income from non-consolidated entities	$ 225,000	$ 284,000