BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Details) (USD $)	3 Months Ended			3 Months Ended			3 Months Ended
	Jul. 31, 2012	Jul. 31, 2011	Apr. 30, 2012	Jul. 31, 2012 Acquired below-market leases and acquired above-market leases [Member]	Jul. 31, 2011 Acquired below-market leases and acquired above-market leases [Member]	Apr. 30, 2012 Acquired below-market leases and acquired above-market leases [Member]	Jul. 31, 2012 Other identified intangible assets [Member]	Jul. 31, 2011 Other identified intangible assets [Member]	Apr. 30, 2011 Other identified intangible assets [Member]	Jul. 31, 2012 Dacotah Bank, Minot, North Dakota [Member]	Jul. 31, 2012 United Community Bank, Minot, North Dakota [Member]	Jul. 31, 2012 Commerce Bank, A Minnesota Banking Corporation [Member]	Jul. 31, 2012 First International Bank, Watford City, North Dakota [Member]	Jul. 31, 2012 Peoples State Bank of Velva, North Dakota [Member]	Jul. 31, 2012 Equity Bank, Minnetonka, Minnesota [Member]	Jul. 31, 2012 Associated Bank, Green Bay, Wisconsin [Member]	Jul. 31, 2012 Venture Bank, Eagan, Minnesota [Member]	Jul. 31, 2012 American National Bank, Omaha, Nebraska [Member]	Jul. 31, 2012 United Community Bank and Equity Bank [Member]
BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES [Abstract]
Interest in operating partnership (in hundredths)	81.30%		81.50%
Redemption basis	one-for-one
Redemptions by limited partner, maximum	2
Number of units to redeem, minimum (in units)	1,000
Period to hold the beneficial interest, minimum	1 year
Real Estate Properties [Line Items]
Impairment of retail property	$ 0	$ 0
Goodwill impairment	0
Compensating Balances [Line Items]
Compensating balances										350,000	275,000	250,000	6,100,000	225,000	300,000	500,000	500,000	400,000
Certificates of deposit																			635,000
Remaining terms of certificates of deposit	2 years
Decrease in lender holdbacks	624,000	924,000
IDENTIFIED INTANGIBLE ASSETS AND INTANGIBLE LIABILITIES AND GOODWILL [Abstract]
Finite-lived Intangible Assets Acquired	752,000	0
Addition to intangible liabilities	0	0
Weighted average lives of intangible assets and intangible liabilities	6 months
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross, Total	93,153,000		92,401,000
Finite-Lived Intangible Assets, Accumulated Amortization	(49,357,000)		(47,813,000)
Finite-Lived Intangible Assets, Net, Total	43,796,000		44,588,000
Indentified intangible liabilities, gross	1,104,000		1,104,000
Indentified intangible liabilities, accumulated amortization	(979,000)		(967,000)
Indentified intangible liabilities, net	125,000		137,000
Amortization of Intangible Assets				(7,000,000)	(26,000,000)		1,500,000	1,700,000
Estimated annual amortization [Abstract]
2014						35,000			4,182,000
2015						18,000			3,825,000
2016						14,000			3,608,000
2017						6,000			3,139,000
2018						(5,000)			2,652,000
Goodwill	1,120,000		1,120,000
Goodwill impairment	0
RECLASSIFICATIONS [Abstract]
Number of apartment complexes sold	2
Number of retail properties sold	1
INVOLUNTARY CONVERSION OF ASSETS [Abstract]
Expensed flood and fire insurance deductibles		400,000
Number of 32-unit buildings		2
Number of units in building	32
Number of buildings destroyed	1
Deductible amount for losses to be covered under insurance policy	200,000
Insurance proceeds received for flood clean up costs and redevelopment			5,700,000
Insurance proceeds received for reimbursement for business interruption (loss of rents)			666,000
Estimated gain on involuntary conversion	$ 274,000