CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Cash Flows from Operating Activities
Net income	$ 18,603,594	$ 9,889,537	$ 15,627,834
Adjustments to reconcile net income to net cash provided by operating activities
Depreciation	5,792,281	6,055,225	5,810,159
Amortization	1,712,530	1,105,087	409,920
Stock-based compensation	1,657,209	1,364,280	1,166,656
Impairment charge	0	13,500,000	8,140,000
Gain on extinguishment of debt	0	(2,360,231)	0
Gain on sale of assets	(2,097,105)	(110,212)	(4,737,968)
(Increase) decrease in accounts receivable	(1,358,374)	528,448	656,707
(Increase) decrease in other assets	(864,294)	8,072	(114,467)
(Decrease) increase in accounts payable	(1,358,147)	1,951,420	(101,367)
Decrease in deferred revenue	(463,380)	(6,951,591)	(689,550)
Increase (decrease) in accrued interest	(398,779)	513,041	(39,858)
Increase (decrease) in tenant deposits	(19,814)	3,873	(16,883)
Net Cash Provided by Operating Activities	21,205,721	25,496,949	26,111,183
Cash Flows from Investing Activities
Acquisition of real estate investments (including capitalized interest of $149,054 in 2012, $0 in 2011, and $319,235 in 2010)	(84,516,078)	(37,113,613)	(47,024,502)
Payment of leasing costs	(55,960)	(197,259)	(368,167)
Net proceeds from sale of assets	15,315,728	8,058,520	14,204,502
Net Cash Used In Investing Activities	(69,256,310)	(29,252,352)	(33,188,167)
Cash Flows from Financing Activities
Proceeds from common stock offering	35,042,235	0	31,072,752
Line-of-credit borrowings	101,220,945	119,244,291	46,896,908
Line-of-credit repayments	(114,134,838)	(91,180,647)	(47,516,654)
Mortgage proceeds	48,640,000	0	0
Payments of mortgages payable	(3,164,654)	(4,229,352)	(4,026,022)
Dividends paid	(17,663,808)	(16,803,705)	(18,344,672)
Limited partners' distributions paid	(556,188)	(594,427)	(709,143)
Repayments of payables for capital expenditures	(424,321)	(286,078)	(352,430)
Payments for financing costs	(1,641,418)	(985,297)	(39,149)
Net Cash Provided by Financing Activities	47,317,953	5,164,785	6,981,590
Net Increase (Decrease) in Cash and Cash Equivalents	(732,636)	1,409,382	(95,394)
Cash and Cash Equivalents, beginning of period	2,002,663	593,281	688,675
Cash and Cash Equivalents, end of period	1,270,027	2,002,663	593,281
Supplemental Disclosure of Cash Flow Information
Cash paid for interest (net of amounts capitalized)	4,722,042	4,458,292	4,487,923
Cash paid for income tax	318,289	220,202	293,720
Supplemental Disclosure of Non-Cash Investing and Financing Activities
Shares issued under Stock Incentive Plan	2,175,831	2,312,056	2,068,866
Dividends and limited partners' distributions declared and unpaid	4,710,446	4,070,690	5,145,740
Real estate investments financed with accounts payable	122,080	424,321	286,078
Forgiveness of mortgage debt	9,173,789	0	0
Real estate acquisitions financed with debt assumption	$ 18,220,528	$ 3,403,603	$ 0