Shareholders' Equity (Details Narrative) - USD ($)			6 Months Ended
	Jun. 15, 2018	Jan. 22, 2018	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Proceed from dividend reinvestment and stock purchase plan (DRIP)			$ 1,590,384	$ 1,386,320
Net proceeds from issuance of shares			$ 48,247,280
Common stock shares authorized			111,363,800		113,663,800
Excess stock, shares authorized			3,000,000		3,000,000
Common Stock [Member]
Dividends paid			$ 13,093,280
Proceed from dividend reinvestment and stock purchase plan (DRIP)			1,590,384
New shares issued under DRIP, value			$ 16,407,829
New shares issued under DRIP			1,281,901
8.0% Series B Cumulative Redeemable Preferred Stock [Member]
Dividends paid	$ 1,900,600
Dividend declared per share, paid	$ 0.50
Annual rate on dividend per share payable quarterly	$ 2.00
Record date of dividend	May 15, 2018
Cumulative redeemable preferred stock percentage	8.00%
Preferred Stock, Liquidation Preference Per Share	$ 25.00
6.75% Series C Cumulative Redeemable Preferred Stock [Member]
Dividends paid	$ 2,425,781
Dividend declared per share, paid	$ 0.421875
Annual rate on dividend per share payable quarterly	$ 1.6875
Record date of dividend	May 15, 2018
Cumulative redeemable preferred stock percentage	6.75%
Preferred Stock, Liquidation Preference Per Share	$ 25.00
6.375% Series D Cumulative Redeemable Preferred Stock [Member]
Dividends paid	$ 796,876
Dividend declared per share, paid	$ 0.3984375
Record date of dividend	May 15, 2018
Preferred Stock, Liquidation Preference Per Share		$ 25.00
Cumulative redeemable preferred stock, shares issued		2,000,000
Percentage rate on cumulative redeemable preferred stock		6.375%
Cumulative redemption price per share		$ 25.00	$ 25.00
Number of sale of shares		$ 2,000,000
Net proceeds from issuance of shares		$ 48,200,000
Description of preferred stock dividend		Annual rate of $1.59375 per share and will be payable quarterly in arrears on March 15, June 15, September 15, and December 15
Preferred stock par value			$ 0.10
Preferred stock redeemable date			Jan. 22, 2023
Series D Preferred Stock [Member]
Common stock shares authorized			2,300,000
Cumulative redeemable preferred stock, authorized			2,300,000
Series B Preferred Stock [Member]
Cumulative redeemable preferred stock, authorized			4,000,000
Series C Preferred Stock [Member]
Cumulative redeemable preferred stock, authorized			5,750,000
July 2, 2018 [Member] | 8.0% Series B Cumulative Redeemable Preferred Stock [Member]
Dividend declared per share, paid			$ 0.50
Dividend paid date			Sep. 17, 2018
Record date of dividend			Aug. 15, 2018
July 2, 2018 [Member] | 6.75% Series C Cumulative Redeemable Preferred Stock [Member]
Dividend declared per share, paid			$ 0.421875
Dividend paid date			Sep. 17, 2018
Record date of dividend			Aug. 15, 2018
July 2, 2018 [Member] | 6.375% Series D Cumulative Redeemable Preferred Stock [Member]
Dividend declared per share, paid			$ 0.3984375
Dividend paid date			Sep. 17, 2018
Record date of dividend			Aug. 15, 2018
Common Stock [Member]
Dividends paid	$ 6,600,505
Dividend declared per share, paid	$ 0.18
Proceed from dividend reinvestment and stock purchase plan (DRIP)	$ 895,984
Record date of dividend	Jun. 15, 2018
Common Stock [Member] | July 2, 2018 [Member]
Annual rate on dividend per share payable quarterly			$ 0.18
Dividend paid date			Sep. 17, 2018
Record date of dividend			Aug. 15, 2018
8.0% Series B Cumulative Redeemable Preferred Stock [Member] | Series B Preferred Shareholders [Member]
Dividends paid			$ 3,801,200
6.75% Series C Cumulative Redeemable Preferred Stock [Member] | Series C Preferred Shareholders [Member]
Dividends paid			4,851,563
6.375% Series D Cumulative Redeemable Preferred Stock [Member] | Series D Preferred Shareholders [Member]
Dividends paid			$ 1,151,042