Shareholders' Equity (Details Narrative) - USD ($)							3 Months Ended		9 Months Ended
	Sep. 15, 2017	Aug. 31, 2017	Aug. 15, 2017	Aug. 02, 2017	Jul. 26, 2017	Jun. 05, 2017	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Proceeds from issuance of offering									$ 22,527,507	$ 0
Proceed from dividend reinvestment and stock purchase plan (DRIP)									2,181,064	1,738,947
Preferred stock redemption charge							$ 0		0		$ 91,595,000
Preferred stock dividends							$ 4,938,937	$ 3,789,747	12,518,431	10,313,685
Net proceeds from issuance of shares									$ 138,983,808	$ 49,120,853
Common stock shares authorized							113,663,800		113,663,800		75,000,000
Excess stock, shares authorized							3,000,000		3,000,000		3,000,000
DRIP [Member]
New shares issued under DRIP, value									$ 48,746,736
New shares issued under DRIP									3,293,638
Common Stock [Member]
Proceed from dividend reinvestment and stock purchase plan (DRIP)									$ 2,181,064
Common Stock [Member] | Maryland State Department of Assessments and Taxation [Member]
Excess stock, shares authorized							85,000,000		85,000,000
8.25% Series A Cumulative Redeemable Preferred Stock [Member]
Dividends paid		$ 1,889,147
Dividend declared per share, paid		$ 0.515625							$ 1.546875
Dividend paid date		Sep. 15, 2017
Record date of dividend		Aug. 15, 2017
Cumulative redeemable preferred stock, authorized		3,663,800
Cumulative redeemable preferred stock percentage		8.25%
Preferred Stock, Liquidation Preference Per Share		$ 25.00
Preferred stock, redemption price per share		$ 25.00
Preferred stock redemption charge		$ 91,595,000
Preferred stock dividends									$ 5,667,441
8.25% Series A Cumulative Redeemable Preferred Stock [Member] | Board of Directors [Member]
Preferred stock redemption charge		$ 3,502,000
8.0% Series B Cumulative Redeemable Preferred Stock [Member]
Dividends paid	$ 1,900,600								$ 5,701,800
Dividend declared per share, paid	$ 0.50
Annual rate on dividend per share payable quarterly	$ 2.00
Record date of dividend	Aug. 15, 2017
Cumulative redeemable preferred stock percentage	8.00%
Preferred Stock, Liquidation Preference Per Share	$ 25.00
6.75% Series C Cumulative Redeemable Preferred Stock [Member]
Number of stock sold during period					5,000,000
Proceeds from issuance of offering					$ 120,800,000
Dividends paid					$ 970,312
Dividend declared per share, paid					$ 0.16875
Annual rate on dividend per share payable quarterly					$ 1.6875
Dividend paid date					Sep. 15, 2017
Record date of dividend					Aug. 31, 2017
Preferred Stock, Liquidation Preference Per Share					$ 25.00
Preferred stock, redemption price per share					$ 25.00
Cumulative redeemable preferred stock, shares issued					5,000,000
Exercised overallotment option and purchased additional shares				750,000
Net proceeds from issuance of shares				$ 18,200,000
Description of preferred stock dividend					Annual rate of $1.6875 per share and will be payable quarterly in arrears on March 15, June 15, September 15, and December 15.
Series A Cumulative Redeemable Preferred Stock [Member]
Cumulative redeemable preferred stock, authorized							3,663,800		3,663,800
Cumulative redeemable preferred stock, shares issued							0		0		3,663,800
Preferred stock, shares outstanding		3,663,800					0		0		3,663,800
Preferred stock par value							$ 0.10		$ 0.10		$ 0.10
Increase in authorized number of shares									113,663,800
Series C Preferred Stock [Member]
Preferred stock, redemption price per share							25.00		$ 25.00
Preferred stock par value							$ 0.10		$ 0.10
Common stock shares authorized							110,000,000		110,000,000
Series C Preferred Stock [Member] | Maryland State Department of Assessments and Taxation [Member]
Increase in authorized number of shares									30,750,000
Excess stock, shares authorized							95,663,800		95,663,800
Series C Preferred Stock [Member] | Maryland State Department of Assessments and Taxation [Member] | Maximum [Member]
Increase in authorized number of shares									126,413,800
Series A Preferred Shares [Member]
Cumulative redeemable preferred stock, authorized							3,663,800		3,663,800
Series A Preferred Shares [Member] | Maximum [Member]
Common stock shares authorized							115,750,000		115,750,000
Series B Preferred Shares [Member]
Cumulative redeemable preferred stock, authorized							4,000,000		4,000,000
Excess stock, shares authorized							3,000,000		3,000,000
Series B Preferred Shares [Member] | Maximum [Member]
Cumulative redeemable preferred stock, authorized							4,000,000		4,000,000
Excess stock, shares authorized							3,000,000		3,000,000
Series C Preferred Shares [Member]
Cumulative redeemable preferred stock, authorized							5,750,000		5,750,000
Excess stock, shares authorized							3,000,000		3,000,000
Series B Preferred Shares One [Member]
Cumulative redeemable preferred stock, authorized							4,000,000		4,000,000
October 2, 2017 [Member] | 8.0% Series B Cumulative Redeemable Preferred Stock [Member]
Dividend declared per share, paid									$ 0.50
Dividend paid date									Dec. 15, 2017
Record date of dividend									Nov. 15, 2017
October 2, 2017 [Member] | Series C Preferred Stock [Member]
Dividend declared per share, paid									$ 0.421875
Dividend paid date									Dec. 15, 2017
Record date of dividend									Nov. 15, 2017
Common Stock [Member]
Number of stock sold during period						1,400,000
Sale of stock price per share						$ 16.60
Proceeds from issuance of offering						$ 22,500,000
Common Stock [Member] | October 2, 2017 [Member]
Annual rate on dividend per share payable quarterly							$ 0.18		$ 0.18
Dividend paid date									Dec. 15, 2017
Record date of dividend									Nov. 15, 2017
Common Stock [Member] | Common Shareholders [Member]
Dividends paid	$ 6,188,961								$ 17,305,824
Dividend declared per share, paid	$ 0.18
Proceed from dividend reinvestment and stock purchase plan (DRIP)			$ 794,744						$ 2,181,064