SUBSEQUENT EVENTS (Details) (USD $)	3 Months Ended		6 Months Ended
	Oct. 31, 2012	Oct. 31, 2011	Oct. 31, 2012	Oct. 31, 2011
Subsequent Event [Line Items]
Shares issued			$ 2,846,000	$ 773,000
Common stock, dividends, per share, declared (in dollars per share)	$ 0.1300	$ 0.1300	$ 0.2600	$ 0.3015
Sales price			8,223,000
Proceeds from sale of property			3,267,000	2,088,000
Subsequent Event [Member] | Multi-family residential property in Topeka, Kansas [Member]
Subsequent Event [Line Items]
Sales price			2,000,000
Buyer's assumption of the existing mortgage debt	1,200,000		1,200,000
Proceeds from sale of property			701,000
Number of buildings	12		12
Area of land (in acres)	5.9		5.9
Number of property unit	116		116
Cash paid for acquisition of property	7,600,000		7,600,000
Subsequent Event [Member] | Multi-family residential property in Omaha, Nebraska [Member]
Subsequent Event [Line Items]
Number of buildings	9		9
Purchase price of acquired property	28,600,000		28,600,000
Area of land (in acres)	18.5		18.5
Number of property unit	336		336
Subsequent Event [Member] | Adjoining parcels of vacant land in Rochester, Minnesota [Member]
Subsequent Event [Line Items]
Purchase price of acquired property	1,100,000		1,100,000
Area of land (in acres)	24		24
Number of property unit	2		2
Subsequent Event [Member] | Vacant land in Grand Forks, North Dakota [Member]
Subsequent Event [Line Items]
Purchase price of acquired property	1,600,000		1,600,000
Area of land (in acres)	10		10
Number of property unit	2		2
Subsequent Event [Member] | Vacant land in Rapid City, South Dakota [Member]
Subsequent Event [Line Items]
Purchase price of acquired property	$ 879,000		$ 879,000
Area of land (in acres)	9		9