Subsequent Events (Details Narrative) - USD ($)				12 Months Ended
	Jan. 22, 2018	Apr. 05, 2016	Oct. 20, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net proceeds from issuance of shares				$ 138,975,847	$ 49,120,853	$ 43,042,124
Common stock, shares authorized				113,663,800	75,000,000
Excess stock, shares authorized				3,000,000	3,000,000
Maryland State Department of Assessments and Taxation [Member]
Increase in authorized number of shares			22,000,000
Common stock, shares authorized			48,663,800
Series B Preferred Stock [Member]
Number of stock sold during period		2,000,000
Subsequent Event [Member] | Maryland State Department of Assessments and Taxation [Member]
Common stock, shares authorized	111,363,800
Excess stock, shares authorized	3,000,000
Subsequent Event [Member] | 6.375% Series D Cumulative Redeemable Preferred Stock [Member]
Number of stock sold during period	2,000,000
Preferred stock, redemption price per share	$ 25.00
Net proceeds from issuance of shares	$ 48,100,000
Subsequent Event [Member] | Series D Preferred Stock [Member] | Maryland State Department of Assessments and Taxation [Member]
Increase in authorized number of shares	2,300,000
Preferred stock, shares authorized	2,300,000
Subsequent Event [Member] | Series B Preferred Stock [Member] | Maryland State Department of Assessments and Taxation [Member]
Preferred stock, shares authorized	4,000,000
Subsequent Event [Member] | Series C Preferred Stock [Member] | Maryland State Department of Assessments and Taxation [Member]
Preferred stock, shares authorized	5,750,000