SUBSEQUENT EVENTS (Details) (USD $)	3 Months Ended				3 Months Ended													3 Months Ended
	Jul. 31, 2013	Jul. 31, 2012	Jul. 31, 2013 Subsequent Event [Member]	Aug. 30, 2013 Subsequent Event [Member]	Jul. 31, 2013 Subsequent Event [Member] Anoka, Minnesota [Member]	Jul. 31, 2013 Subsequent Event [Member] Duluth, Minnesota [Member]	Jul. 31, 2013 Subsequent Event [Member] Sioux Falls, South Dakota, 1 [Member]	Jul. 31, 2013 Subsequent Event [Member] Sioux Falls, South Dakota, 2 [Member]	Jul. 31, 2013 Subsequent Event [Member] Minneapolis, Minnesota [Member] sqft	Jul. 31, 2013 Subsequent Event [Member] Grand Forks Grand Forks, ND [Member]	Aug. 09, 2013 Subsequent Event [Member] Jamestown, North Dakota [Member] acre	Jul. 31, 2013 Subsequent Event [Member] Sartell, Minnesota [Member]	Jul. 31, 2013 Subsequent Event [Member] Monticello, Minnesota [Member] acre	Jul. 31, 2013 Subsequent Event [Member] Rapid City, South Dakota 1 [Member]	Jul. 31, 2013 Subsequent Event [Member] Rapid City, South Dakota 1 [Member] Sioux Falls, South Dakota, 1 [Member] acre	Jul. 31, 2013 Subsequent Event [Member] Rapid City, South Dakota 2 [Member]	Jul. 31, 2013 Subsequent Event [Member] Rapid City, South Dakota 2 [Member] Sioux Falls, South Dakota, 2 [Member] acre	Jul. 31, 2013 Subsequent Event [Member] Series A Preferred Stock [Member]	Jul. 31, 2013 Subsequent Event [Member] Series A Preferred Stock [Member] Dividend Declared [Member]	Jul. 31, 2013 Subsequent Event [Member] Series B Preferred Stock [Member]	Jul. 31, 2013 Subsequent Event [Member] Series B Preferred Stock [Member] Dividend Declared [Member]
Subsequent Event [Line Items]
Distributions, common shares and units (in dollars per share)	$ 0.1300	$ 0.1300
Distributions, Redeemable Preferred Shares (in dollars per share)																			$ 51.56		$ 49.68
Dividends date declared			Sep. 04, 2013															Sep. 04, 2013		Sep. 04, 2013
Dividends date of record			Sep. 16, 2013															Sep. 16, 2013		Sep. 16, 2013
Dividends date to be paid			Oct. 01, 2013															Sep. 30, 2013		Sep. 30, 2013
Area of land (in acres)											9.2		5.0		5.2		5.6
Area of property (square feet)									10,000
Sales price of property					$ 325,000	$ 1,800,000	$ 2,200,000	$ 1,300,000
Cash paid for acquisition of property											700,000	15,200,000	656,000	657,000		707,000
Number of units									130	251		121
Interest in joint venture (in hundredths)									58.60%
Interest in joint venture, remaining percentage (in hundredths)									41.40%
Estimated cost of construction									29,000,000	39,000,000
Purchase price of acquired property										1,600,000
Construction loan for joint venture project									21,700,000	14,500,000
Maximum value of shares of beneficial interest under the agreement				$ 75.0
Shares issued, under the agreement				0