CONDENSED CONSOLIDATED BALANCE SHEETS (Unaudited) (Parenthetical) - USD ($)	Jan. 31, 2016	Apr. 30, 2015
ASSETS
Intangible assets, accumulated amortization	$ 21,214,000	$ 19,610,000
Property and equipment, accumulated depreciation	1,116,000	1,464,000
Deferred charges and leasing costs, accumulated amortization	$ 9,078,000	$ 8,077,000
EQUITY
Common Shares of Beneficial Interest, no par value (in dollars per share)	$ 0	$ 0
Common Shares of Beneficial Interest, shares issued (in shares)	121,033,647	124,455,624
Common Shares of Beneficial Interest, shares outstanding (in shares)	121,033,647	124,455,624
Noncontrolling interests - Operating Partnership (in shares)	13,863,575	13,999,725
Receivable Arising from Straight-Lining of Rents [Member]
ASSETS
Accounts receivable, allowance	$ 766,000	$ 718,000
Accounts Receivable [Member]
ASSETS
Accounts receivable, allowance	$ 163,000	$ 438,000
Preferred Series A [Member]
EQUITY
Preferred Shares of Beneficial Interest, no par value (in dollars per share)	$ 0	$ 0
Preferred Shares of Beneficial Interest, shares issued (in shares)	1,150,000	1,150,000
Preferred Shares of Beneficial Interest, shares outstanding (in shares)	1,150,000	1,150,000
Preferred Shares of Beneficial Interest, aggregate liquidation preference	$ 28,750,000	$ 28,750,000
Preferred Series B [Member]
EQUITY
Preferred Shares of Beneficial Interest, no par value (in dollars per share)	$ 0	$ 0
Preferred Shares of Beneficial Interest, shares issued (in shares)	4,600,000	4,600,000
Preferred Shares of Beneficial Interest, shares outstanding (in shares)	4,600,000	4,600,000
Preferred Shares of Beneficial Interest, aggregate liquidation preference	$ 115,000,000	$ 115,000,000