Consolidated Balance Sheets (Parenthetical) - $ / shares	Mar. 31, 2019	Dec. 31, 2018
Common stock, par value	$ 0.10	$ 0.10
Common stock, shares authorized	111,363,800	111,363,800
Common stock, shares issued	39,158,261	38,320,414
Common stock, shares outstanding	39,158,261	38,320,414
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 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	5,750,000
Cumulative redeemable preferred stock, shares issued	5,750,000	5,750,000
Cumulative redeemable preferred stock, shares outstanding	5,750,000	5,750,000
Series D Cumulative Redeemable Preferred Stock [Member]
Percentage rate on cumulative redeemable preferred stock	6.375%	6.375%
Cumulative redeemable preferred stock, par value	$ 0.10	$ 0.10
Cumulative redeemable preferred stock, shares authorized	2,300,000	2,300,000
Cumulative redeemable preferred stock, shares issued	2,000,000	2,000,000
Cumulative redeemable preferred stock, shares outstanding	2,000,000	2,000,000