CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $)	6 Months Ended
	Oct. 31, 2012	Oct. 31, 2011
CASH FLOWS FROM OPERATING ACTIVITIES
Net income	$ 12,006,000	$ 3,064,000
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	33,730,000	30,662,000
Gain on sale of real estate, land, other investments and discontinued operations	(2,680,000)	(589,000)
Gain on involuntary conversion	(2,263,000)	0
Impairment of real estate assets	0	0
Bad debt expense	694,000	413,000
Changes in other assets and liabilities:
Increase in receivable arising from straight-lining of rents	(1,743,000)	(2,105,000)
Decrease (increase) in accounts receivable	2,857,000	(2,785,000)
Decrease in prepaid and other assets	1,598,000	633,000
Decrease (increase) in tax, insurance and other escrow	161,000	(427,000)
Increase in deferred charges and leasing costs	(2,290,000)	(3,422,000)
Decrease in accounts payable, accrued expenses, and other liabilities	(7,096,000)	(1,234,000)
Net cash provided by operating activities	34,974,000	24,210,000
CASH FLOWS FROM INVESTING ACTIVITIES
Proceeds from real estate deposits	1,093,000	1,431,000
Payments for real estate deposits	(885,000)	(1,553,000)
Principal proceeds on mortgage loans receivable	0	1,000
Increase in other investments	0	(3,000)
Decrease in lender holdbacks for improvements	1,018,000	5,000,000
Increase in lender holdbacks for improvements	(1,687,000)	(620,000)
Proceeds from sale of discontinued operations	3,267,000	2,088,000
Proceeds from sale of real estate and other investments	0	284,000
Insurance proceeds received	3,432,000	4,148,000
Payments for acquisitions and improvements of real estate assets	(81,820,000)	(77,100,000)
Net cash used by investing activities	(75,582,000)	(66,324,000)
CASH FLOWS FROM FINANCING ACTIVITIES
Proceeds from mortgages payable	57,030,000	70,745,000
Principal payments on mortgages payable	(68,384,000)	(39,303,000)
Proceeds from revolving line of credit and other debt	24,400,000	17,000,000
Principal payments on revolving line of credit and other debt	(34,500,000)	(10,000)
Proceeds from sale of common shares, net of issue costs	2,448,000	330,000
Proceeds from sale of common shares under distribution reinvestment and share purchase program	17,979,000	11,672,000
Repurchase of fractional shares and partnership units	(15,000)	(8,000)
Distributions paid to common shareholders, net of reinvestment of $10,177, $10,627 and $9,762, respectively	(17,610,000)	(19,622,000)
Distributions paid to preferred shareholders	(2,710,000)	(1,186,000)
Distributions paid to noncontrolling interests - Unitholders of the Operating Partnership, net of reinvestment of $313 and $360, respectively	(5,118,000)	(5,609,000)
Distributions paid to noncontrolling interests - consolidated real estate entities	0	(362,000)
Distributions paid to redeemable noncontrolling interests - consolidated real estate entities	0	(27,000)
Net cash provided by financing activities	84,877,000	33,620,000
Statement [Line Items]
Proceeds from underwritten Public Offering of Preferred Shares - Series B, net of offering costs	2,846,000	773,000
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	44,269,000	(8,494,000)
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD	39,989,000	41,191,000
CASH AND CASH EQUIVALENTS AT END OF PERIOD	84,258,000	32,697,000
SUPPLEMENTARY SCHEDULE OF NON-CASH INVESTING AND FINANCING
Distribution reinvestment plan	6,129,000	4,870,000
Operating partnership distribution reinvestment plan	313,000	360,000
Operating partnership units converted to shares	579,000	3,454,000
Shares issued under the Incentive Award Plan	398,000	443,000
Real estate assets acquired through the issuance of operating partnership units	8,116,000	1,974,000
Real estate assets acquired through assumption of indebtedness and accrued costs	12,500,000	7,190,000
Mortgages included in real estate dispositions	4,638,000	0
Adjustments to accounts payable included within real estate investments	(1,974,000)	(2,780,000)
Noncontrolling partnership interest	1,136,000	2,227,000
Fair value adjustments to redeemable noncontrolling interests	0	35,000
Involuntary conversion of assets due to flood and fire damage	107,000	2,638,000
Construction debt reclassified to mortgages payable	0	7,190,000
Cash paid during the year for:
Interest on mortgages	30,980,000	29,894,000
Interest other	881,000	1,361,000
Cash paid during the period, total	31,861,000	31,255,000
Preferred Class B [Member]
Statement [Line Items]
Proceeds from underwritten Public Offering of Preferred Shares - Series B, net of offering costs	$ 111,357,000	$ 0