Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2017	Dec. 31, 2016
Common stock, par value	$ 0.10	$ 0.10
Common stock, shares authorized	113,663,800	75,000,000
Common stock, shares issued	35,488,068	29,388,811
Common stock, shares outstanding	35,488,068	29,388,811
Excess stock, par value	$ 0.10	$ 0.10
Excess stock, shares authorized	3,000,000	3,000,000
Excess stock, shares issued
Excess stock, shares outstanding
Series A Cumulative Redeemable Preferred Stock [Member]
Percentage rate on cumulative redeemable preferred stock	8.25%	8.25%
Cumulative redeemable preferred stock, par value	$ 0.10	$ 0.10
Cumulative redeemable preferred stock, shares authorized	0	3,663,800
Cumulative redeemable preferred stock, shares issued	0	3,663,800
Cumulative redeemable preferred stock, shares outstanding	0	3,663,800
Series B Cumulative Redeemable Preferred Stock [Member]
Percentage rate on cumulative redeemable preferred stock	8.00%	8.00%
Cumulative redeemable preferred stock, par value	$ 0.10	$ 0.10
Cumulative redeemable preferred stock, shares authorized	4,000,000	4,000,000
Cumulative redeemable preferred stock, shares issued	3,801,200	3,801,200
Cumulative redeemable preferred stock, shares outstanding	3,801,200	3,801,200
Series C Cumulative Redeemable Preferred Stock [Member]
Percentage rate on cumulative redeemable preferred stock	6.75%	6.75%
Cumulative redeemable preferred stock, par value	$ 0.10	$ 0.10
Cumulative redeemable preferred stock, shares authorized	5,750,000	0
Cumulative redeemable preferred stock, shares issued	5,750,000	0
Cumulative redeemable preferred stock, shares outstanding	5,750,000	0