CONDENSED CONSOLIDATED BALANCE SHEETS (unaudited) (Parenthetical) - USD ($) shares in Thousands, $ in Thousands	Jul. 31, 2017	Apr. 30, 2017
Other assets
Intangible assets, accumulated amortization	$ 5,724	$ 5,444
Property and equipment, accumulated depreciation	1,216	1,199
Deferred charges and leasing costs, accumulated amortization	4,619	4,275
LIABILITIES
Mortgages payable, loan costs	$ 3,276	$ 3,480
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest [Abstract]
Common Shares of Beneficial Interest, no par value (in dollars per share)	$ 0	$ 0
Common Shares of Beneficial Interest, shares issued (in shares)	120,587	121,199
Common Shares of Beneficial Interest, shares outstanding (in shares)	120,587	121,199
Noncontrolling interests - Operating Partnership (in shares)	14,657	15,617
Receivable Arising from Straight-Lining of Rents [Member]
Other assets
Accounts receivable, allowance	$ 285	$ 340
Accounts Receivable [Member]
Other assets
Accounts receivable, allowance	$ 182	$ 210
Series B Preferred Stock [Member]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest [Abstract]
Preferred Shares of Beneficial Interest, par value (in dollars per share)	$ 0	$ 0
Preferred Shares of Beneficial Interest, shares issued (in shares)	4,600	4,600
Preferred Shares of Beneficial Interest, shares outstanding (in shares)	4,600	4,600
Preferred shares liquidation preference	$ 115,000	$ 115,000