Shareholders' Equity (Details Narrative) - USD ($)												3 Months Ended												9 Months Ended	12 Months Ended			14 Months Ended
	Sep. 17, 2018	Jan. 22, 2018	Aug. 31, 2017	Aug. 02, 2017	Jul. 26, 2017	Jun. 05, 2017	Jun. 02, 2017	Aug. 11, 2016	Apr. 05, 2016	Apr. 04, 2016	Oct. 20, 2015	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2016
Preferred stock redemption charge												$ 95,030,000				$ 95,030,000									$ 95,030,000	$ 95,030,000
Dividend declared per share, paid												$ 0.18	$ 0.18	$ 0.18	$ 0.18	$ 0.18	$ 0.18	$ 0.18	$ 0.18	$ 0.18	$ 0.18	$ 0.18	$ 0.18		$ 0.72	$ 0.72	$ 0.72
Dividend paid date																									Feb. 15, 2019
Record date of dividend																									Mar. 15, 2019
Net proceeds from issuance of shares																									$ 48,247,280	$ 138,975,847	$ 49,120,853
Common stock shares authorized										81,663,800		111,363,800				113,663,800									111,363,800	113,663,800
Excess stock, shares authorized												3,000,000				3,000,000									3,000,000	3,000,000
January 15, 2019 [Member]
Number of share authorized to repurchase under share repurchase program												25,000,000													25,000,000
Amendment [Member]
Excess stock, shares authorized										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
Excess stock, shares authorized											3,000,000
Maryland State Department of Assessments and Taxation [Member] | Amendment [Member]
Increase in authorized number of shares							10,000,000
Common stock shares authorized								85,663,800
Excess stock, shares authorized								3,000,000		3,000,000
8.25% Series A Cumulative Redeemable Preferred Stock [Member]
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
Dividends paid			$ 1,889,147																							$ 3,502,000
Dividend declared per share, paid			$ 0.515625
Dividend paid date			Sep. 15, 2017
Record date of dividend			Aug. 15, 2017
Series B Cumulative Redeemable Preferred Stock [Member]
Cumulative redeemable preferred stock, authorized					4,000,000
Dividends paid																												$ 710,610
Dividend paid date																												Mar. 15, 2016
Cumulative redeemable preferred stock, shares issued											1,801,200	3,801,200				3,801,200									3,801,200	3,801,200
Percentage rate on cumulative redeemable preferred stock											8.00%	8.00%				8.00%									8.00%	8.00%
Cumulative redemption price per share											$ 25.00
Net proceeds from issuance of shares											$ 43,000,000
Description of preferred stock dividend											Annual rate of $2.00 per share and will be payable quarterly in arrears at March 15, June 15, September 15, and December 15.
Preferred stock par value											$ 0.10	$ 0.10				$ 0.10									$ 0.10	$ 0.10
Shares issued price per share											$ 25.00
Preferred stock, shares outstanding												3,801,200				3,801,200									3,801,200	3,801,200
Preferred stock, shares authorized		4,000,000										4,000,000				4,000,000									4,000,000	4,000,000
Series B Cumulative Redeemable Preferred Stock [Member] | Maryland State Department of Assessments and Taxation [Member]
Cumulative redeemable preferred stock, authorized										2,000,000
Excess stock, shares authorized										3,000,000
Series B Cumulative Redeemable Preferred Stock [Member] | Maryland State Department of Assessments and Taxation [Member] | Amendment [Member]
Cumulative redeemable preferred stock, authorized								4,000,000
Series B Preferred Stock [Member]
Number of stock sold during period									2,000,000
Sale of stock price per share									$ 25.50
Proceeds from sale of common stock									$ 49,100,000
Series B Preferred Stock [Member] | Amendment [Member]
Cumulative redeemable preferred stock, authorized										4,000,000
Series B Preferred Stock [Member] | Maryland State Department of Assessments and Taxation [Member] | Amendment [Member]
Common stock shares authorized										2,000,000
Series A Cumulative Redeemable Preferred Stock [Member]
Cumulative redeemable preferred stock, authorized			3,663,800		3,663,800
Preferred stock par value					$ 0.10
Increase in authorized number of shares			113,663,800
Series A Cumulative Redeemable Preferred Stock [Member] | Maryland State Department of Assessments and Taxation [Member]
Cumulative redeemable preferred stock, authorized										3,663,800
Series A Cumulative Redeemable Preferred Stock [Member] | Maryland State Department of Assessments and Taxation [Member] | Amendment [Member]
Cumulative redeemable preferred stock, authorized								3,663,800		3,663,800
Series A Preferred Stock [Member] | Amendment [Member]
Cumulative redeemable preferred stock, authorized										3,663,800
Common Stock [Member] | Maryland State Department of Assessments and Taxation [Member]
Common stock shares authorized					85,000,000			71,000,000
Common Stock [Member] | Maryland State Department of Assessments and Taxation [Member] | Amendment [Member]
Common stock shares authorized								75,000,000
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
Preferred stock, liquidation preference per share					$ 25.00
Preferred stock, redemption price per share					$ 25.00
Dividends paid					$ 970,312
Dividend declared per share, paid					$ 0.16875
Dividend paid date					Sep. 15, 2017
Record date of dividend					Aug. 31, 2017
Cumulative redeemable preferred stock, shares issued					5,000,000
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.
Exercised overallotment option and purchased additional shares				750,000
Annual rate on dividend per share payable quarterly					$ 1.6875
Series C Cumulative Redeemable Preferred Stock [Member]
Preferred stock, redemption price per share					25.00
Cumulative redeemable preferred stock, shares issued												5,750,000				5,750,000									5,750,000	5,750,000
Percentage rate on cumulative redeemable preferred stock												6.75%				6.75%									6.75%	6.75%
Preferred stock par value					$ 0.10							$ 0.10				$ 0.10									$ 0.10	$ 0.10
Preferred stock, shares outstanding												5,750,000				5,750,000									5,750,000	5,750,000
Preferred stock, shares authorized												5,750,000				5,750,000									5,750,000	5,750,000
Series C Cumulative Redeemable Preferred Stock [Member] | Maryland State Department of Assessments and Taxation [Member]
Increase in authorized number of shares					30,750,000
Common stock shares authorized					95,663,800
Series A Preferred Shares [Member]
Cumulative redeemable preferred stock, authorized					3,663,800
Series B Preferred Shares [Member]
Cumulative redeemable preferred stock, authorized					4,000,000
Excess stock, shares authorized					3,000,000
Series C Preferred Shares [Member]
Cumulative redeemable preferred stock, authorized					5,750,000
Common stock shares authorized					5,750,000
Excess stock, shares authorized					3,000,000
6.375% Series D Cumulative Redeemable Preferred Stock [Member]
Number of stock sold during period		2,000,000
Proceeds from issuance of offering		$ 48,200,000
Preferred stock, liquidation preference per share		$ 25.00
Preferred stock, redemption price per share		$ 25.00
Dividends paid	$ 796,876
Dividend declared per share, paid	$ 0.3984375
Dividend paid date	Jun. 01, 2018
Record date of dividend	Aug. 15, 2018
Cumulative redeemable preferred stock, shares issued		2,000,000
Description of preferred stock dividend		Arrears on March 15, June 15, September 15, and December 15 at an annual rate of $1.59375 per share.
Excess stock, shares authorized		3,000,000
Series D Preferred Stock [Member]
Preferred stock, redemption price per share		$ 25.00
Dividends paid																								$ 1,947,918
Preferred stock par value		$ 0.10
Common stock shares authorized		111,363,800
Excess stock, shares authorized		3,000,000
Reclassifying shares of common stock		2,300,000
Preferred stock, shares authorized		2,300,000
Series C Preferred Stock [Member]
Preferred stock, shares authorized		5,750,000
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] | Amendment [Member]
Common stock shares authorized										71,000,000
Common Stock [Member] | Maryland State Department of Assessments and Taxation [Member]
Common stock shares authorized											62,000,000
Common Stock [Member] | Series B Cumulative Redeemable Preferred Stock [Member]
Common stock shares authorized											2,000,000
8.25% Series A Cumulative Redeemable Preferred Stock [Member] | Maryland State Department of Assessments and Taxation [Member]
Excess stock, shares authorized											3,000,000
8.25% Series A Cumulative Redeemable Preferred Stock One [Member] | Maryland State Department of Assessments and Taxation [Member]
Cumulative redeemable preferred stock, authorized											3,663,800
Excess stock, shares authorized											3,000,000
8.0% Series B Cumulative Redeemable Preferred Stock [Member] | Maryland State Department of Assessments and Taxation [Member]
Cumulative redeemable preferred stock, authorized											2,000,000
Minimum [Member]
Amount of optional cash payments																									$ 500
Minimum [Member] | Common Stock [Member] | Maryland State Department of Assessments and Taxation [Member]
Common stock shares authorized										62,000,000	42,000,000
Minimum [Member] | 8.25% Series A Cumulative Redeemable Preferred Stock [Member] | Maryland State Department of Assessments and Taxation [Member]
Cumulative redeemable preferred stock, authorized											3,663,800
Minimum [Member] | Common Stock One [Member] | Maryland State Department of Assessments and Taxation [Member]
Common stock shares authorized											64,000,000
Minimum [Member] | 8.25% Series A Cumulative Redeemable Preferred Stock One [Member] | Maryland State Department of Assessments and Taxation [Member]
Cumulative redeemable preferred stock, authorized											3,663,800
Maximum [Member]
Amount of optional cash payments																									$ 1,000
Increase in authorized number of shares										11,000,000
Common stock shares authorized										70,663,800
Maximum [Member] | Maryland State Department of Assessments and Taxation [Member] | Amendment [Member]
Excess stock, shares authorized								3,000,000
Maximum [Member] | Series B Cumulative Redeemable Preferred Stock [Member] | Maryland State Department of Assessments and Taxation [Member] | Amendment [Member]
Cumulative redeemable preferred stock, authorized								4,000,000
Maximum [Member] | Series A Cumulative Redeemable Preferred Stock [Member] | Maryland State Department of Assessments and Taxation [Member] | Amendment [Member]
Cumulative redeemable preferred stock, authorized								3,663,800
Maximum [Member] | Series C Cumulative Redeemable Preferred Stock [Member] | Maryland State Department of Assessments and Taxation [Member]
Increase in authorized number of shares					126,413,800
Maximum [Member] | Series A Preferred Shares [Member]
Common stock shares authorized					115,750,000
Maximum [Member] | Common Stock [Member] | Maryland State Department of Assessments and Taxation [Member]
Increase in authorized number of shares								4,000,000
Common stock shares authorized										73,000,000
Maximum [Member] | Common Stock [Member] | Maryland State Department of Assessments and Taxation [Member] | Amendment [Member]
Common stock shares authorized								81,663,800
Maximum [Member] | Common Stock [Member] | Series A Preferred Shares [Member]
Common stock shares authorized					110,000,000
Maximum [Member] | Common Stock One [Member] | Maryland State Department of Assessments and Taxation [Member]
Common stock shares authorized											70,663,800
Dividend Reinvestment Stock Purchase Plan [Member]
Discount rate on purchase price under dividend reinvestment plan																									95.00%