CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Apr. 30, 2014	Apr. 30, 2013
Other assets
Receivable arising from straight-lining of rents, allowance	$ 796	$ 830
Accounts receivable, allowance	248	563
Intangible assets, accumulated amortization	24,071	27,708
Property and equipment, accumulated depreciation	2,041	1,673
Deferred charges and leasing costs, accumulated amortization	21,068	18,714
Statement [Line Items]
Common Shares of Beneficial Interest, no par value (in dollars per share)	$ 0	$ 0
Common Shares of Beneficial Interest, shares issued (in shares)	109,019,341	101,487,976
Common Shares of Beneficial Interest, shares outstanding (in shares)	109,019,341	101,487,976
Noncontrolling interests - Operating Partnership (in shares)	21,093,445	21,635,127
Preferred Class A [Member]
Statement [Line Items]
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 Class B [Member]
Statement [Line Items]
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