CONDENSED CONSOLIDATED BALANCE SHEETS (unaudited) (Parenthetical) - USD ($) shares in Thousands, $ in Thousands	Jan. 31, 2018	Apr. 30, 2017
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest [Abstract]
Common Shares of Beneficial Interest, shares issued (in shares)	120,035	121,199
Common Shares of Beneficial Interest, shares outstanding (in shares)	120,035	121,199
Noncontrolling interests - Operating Partnership (in shares)	14,168	15,617
Series B Preferred Stock [Member]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest [Abstract]
Preferred Shares of Beneficial Interest, liquidation preference (in dollars per share)	$ 25	$ 25
Preferred Shares of Beneficial Interest, shares issued (in shares)	0	4,600
Preferred Shares of Beneficial Interest, shares outstanding (in shares)	0	4,600
Preferred shares liquidation preference		$ 115,000
Series C Preferred Stock [Member]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest [Abstract]
Preferred Shares of Beneficial Interest, liquidation preference (in dollars per share)	$ 25	$ 25
Preferred Shares of Beneficial Interest, shares issued (in shares)	4,118	0
Preferred Shares of Beneficial Interest, shares outstanding (in shares)	4,118	0
Preferred shares liquidation preference	$ 102,962
Medium-term Notes [Member]
LIABILITIES
Mortgages payable, loan costs	517	$ 0
Mortgages [Member]
LIABILITIES
Mortgages payable, loan costs	$ 2,488	$ 3,054

Number of partnership units held by noncontrolling interests as of the balance sheet date.

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Total number of common shares of an entity that have been sold or granted to shareholders (includes common shares that were issued, repurchased and remain in the treasury). These shares represent capital invested by the firm's shareholders and owners, and may be all or only a portion of the number of shares authorized. Shares issued include shares outstanding and shares held in the treasury.

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Number of shares of common stock outstanding. Common stock represent the ownership interest in a corporation.

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Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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The per share liquidation preference (or restrictions) of nonredeemable preferred stock (or preferred stock redeemable solely at the option of the issuer) that has a preference in involuntary liquidation considerably in excess of the par or stated value of the shares. The liquidation preference is the difference between the preference in liquidation and the par or stated values of the share.

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Value of the difference between preference in liquidation and the par or stated values of the preferred shares.

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Total number of nonredeemable preferred shares (or preferred stock redeemable solely at the option of the issuer) issued to shareholders (includes related preferred shares that were issued, repurchased, and remain in the treasury). May be all or portion of the number of preferred shares authorized. Excludes preferred shares that are classified as debt.

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Aggregate share number for all nonredeemable preferred stock (or preferred stock redeemable solely at the option of the issuer) held by stockholders. Does not include preferred shares that have been repurchased.

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