Discontinued operations (Details) (USD $)	3 Months Ended			6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Mar. 31, 2010	Jun. 30, 2011	Jun. 30, 2010	Dec. 31, 2010
Discontinued operations
Maximum expected period for completion of sale of a real estate property to be classified as held for sale (in years)				1
Income from discontinued operations, net
Total revenue	$ 2,000			$ 2,000	$ 794,000
Operating expenses	40,000	17,000		99,000	216,000
Revenue less operating expenses	(38,000)	(17,000)		(97,000)	578,000
Depreciation expense		43,000			69,000
(Loss) income from discontinued operations before gain on sales of real estate	(38,000)	(60,000)		(97,000)	509,000
Gain on sales of real estate					24,000
(Loss) income from discontinued operations, net	(38,000)	(60,000)		(97,000)	533,000
Net assets of discontinued operations
Properties "held for sale," net	1,859,000			1,859,000		1,859,000
Other assets	117,000			117,000		90,000
Total assets	1,976,000			1,976,000		1,949,000
Total liabilities	157,000			157,000		133,000
Net assets of discontinued operations	1,819,000			1,819,000		1,816,000
Number of operating properties classified as held-for-sale	1	1		1	1
Number of properties sold			1		1
Total sales price for the property sold					$ 11,800,000