Gain on Sales of Investment Properties (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2012 item	Jun. 30, 2011 item	Jun. 30, 2012 item	Jun. 30, 2011 item
Sales of investment properties
Sales proceed				$ 675,000
Gain on sale of land				155,000
New properties and properties under development
Sales of investment properties
Number of properties sold	14	6	19	9
Sales proceed	15,000,000	3,300,000	18,600,000	4,400,000
Gain on sales of investment properties	3,400,000	1,100,000	4,000,000	1,200,000
Excess land
Sales of investment properties
Number of properties sold		3
Sales proceed		675,000
Gain on sale of land		$ 155,000