BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Details) (USD $)	6 Months Ended			3 Months Ended		6 Months Ended			3 Months Ended		6 Months Ended
	Oct. 31, 2012	Oct. 31, 2011	Apr. 30, 2012	Oct. 31, 2012 Acquired below-market leases and acquired above-market leases [Member]	Oct. 31, 2011 Acquired below-market leases and acquired above-market leases [Member]	Oct. 31, 2012 Acquired below-market leases and acquired above-market leases [Member]	Oct. 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]	Oct. 31, 2012 Other identified intangible assets [Member]	Oct. 31, 2011 Other identified intangible assets [Member]	Oct. 31, 2012 Other identified intangible assets [Member]	Oct. 31, 2011 Other identified intangible assets [Member]	Apr. 30, 2011 Other identified intangible assets [Member]	Oct. 31, 2012 Dacotah Bank, Minot, North Dakota [Member]	Oct. 31, 2012 United Community Bank, Minot, North Dakota [Member]	Oct. 31, 2012 Commerce Bank, A Minnesota Banking Corporation [Member]	Oct. 31, 2012 First International Bank, Watford City, North Dakota [Member]	Oct. 31, 2012 Peoples State Bank of Velva, North Dakota [Member]	Oct. 31, 2012 Equity Bank, Minnetonka, Minnesota [Member]	Oct. 31, 2012 Associated Bank, Green Bay, Wisconsin [Member]	Oct. 31, 2012 Venture Bank, Eagan, Minnesota [Member]	Oct. 31, 2012 American National Bank, Omaha, Nebraska [Member]	Oct. 31, 2012 United Community Bank and Equity Bank [Member]
BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES [Abstract]
Interest in common units in operating partnership (in hundredths)	81.40%		81.50%
Interest in preferred units in operating partnership (in hundredths)	100.00%
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														350,000,000	275,000,000	250,000,000	6,100,000	225,000,000	300,000,000	500,000,000	500,000,000	400,000,000
Certificates of deposit																							637,000,000
Remaining terms of certificates of deposit	2 years
Decrease in lender holdbacks	1,018,000	5,000,000
IDENTIFIED INTANGIBLE ASSETS AND INTANGIBLE LIABILITIES AND GOODWILL [Abstract]
Finite-lived Intangible Assets Acquired	813,000,000	416,000,000
Addition to intangible liabilities	0	0
Weighted average lives of intangible assets and intangible liabilities	6 years
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross, Total	67,860,000		92,401,000
Finite-Lived Intangible Assets, Accumulated Amortization	(25,579,000)		(47,813,000)
Finite-Lived Intangible Assets, Net, Total	42,281,000		44,588,000
Indentified intangible liabilities, gross	408,000		1,104,000
Indentified intangible liabilities, accumulated amortization	(294,000)		(967,000)
Indentified intangible liabilities, net	114,000		137,000
Amortization of Intangible Assets				(7,000,000)	(6,000,000)	(14,000,000)	(32,000,000)		1,600,000	1,500,000	3,100,000	3,200,000
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	1,110,000		1,120,000
Goodwill impairment	0
Goodwill derecognized	10,000
RECLASSIFICATIONS [Abstract]
Number of condominiums sold	4
Number of multi-family residential properties sold	2
INVOLUNTARY CONVERSION OF ASSETS [Abstract]
Number of 32-unit buildings	2
Expensed flood and fire insurance deductibles	400,000,000
Deductible amount for losses to be covered under insurance policy			200,000,000
Insurance proceeds received for flood clean up costs and redevelopment			5,700,000
Estimated gain on involuntary conversion	2,300,000		274,000,000
Insurance proceeds received for redevelopment	2,900,000
Insurance proceeds received for business interruption from the flood and fire	409,000
Insurance proceeds received for total business interruption proceeds	666,000
Insurance claim on total business interruption	$ 1,100,000