Shareholders' Equity (Details Narrative) - USD ($)				3 Months Ended
	Mar. 15, 2018	Feb. 15, 2018	Jan. 22, 2018	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Proceed from dividend reinvestment and stock purchase plan (DRIP)				$ 694,400	$ 681,504
Net proceeds from issuance of shares				$ 48,247,280	$ 0
Common stock shares authorized				111,363,800		113,663,800
Excess stock, shares authorized				3,000,000		3,000,000
Common Stock [Member]
Proceed from dividend reinvestment and stock purchase plan (DRIP)				$ 694,400
New shares issued under DRIP, value				$ 10,051,499
New shares issued under DRIP				809,076
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	Feb. 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	Feb. 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	$ 354,166
Dividend declared per share, paid	$ 0.17708333
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
April 2, 2018 [Member] | 8.0% Series B Cumulative Redeemable Preferred Stock [Member]
Dividend declared per share, paid				$ 0.50
Dividend paid date				Jun. 15, 2018
Record date of dividend				May 15, 2018
April 2, 2018 [Member] | 6.75% Series C Cumulative Redeemable Preferred Stock [Member]
Dividend declared per share, paid				$ 0.421875
Dividend paid date				Jun. 15, 2018
Record date of dividend				May 15, 2018
April 2, 2018 [Member] | 6.375% Series D Cumulative Redeemable Preferred Stock [Member]
Dividend declared per share, paid				$ 0.3984375
Dividend paid date				Jun. 15, 2018
Record date of dividend				May 15, 2018
Common Stock [Member]
Dividends paid	$ 6,492,774
Dividend declared per share, paid	$ 0.18
Proceed from dividend reinvestment and stock purchase plan (DRIP)		$ 694,400
Record date of dividend	Feb. 15, 2018
Common Stock [Member] | April 2, 2018 [Member]
Annual rate on dividend per share payable quarterly				$ 0.18
Dividend paid date				Jun. 15, 2018
Record date of dividend				May 15, 2018