Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized	100,000,000	100,000,000
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	500,000,000	500,000,000
Common stock, issued	86,595,735	86,149,720
Common stock, outstanding	86,595,735	86,149,720
9.25% Series A Preferred Stock
Preferred stock, shares authorized	2,000,000	2,000,000
Preferred stock, shares issued	2,000,000	2,000,000
Preferred stock, shares outstanding	2,000,000	2,000,000
Preferred stock, aggregate liquidation preference (in dollars)	$ 50,385	$ 50,398
Preferred stock, dividend rate (as a percent)	9.25%	9.25%
7.875% Series B Preferred Stock
Preferred stock, shares authorized	3,000,000	3,000,000
Preferred stock, shares issued	3,000,000	3,000,000
Preferred stock, shares outstanding	3,000,000	3,000,000
Preferred stock, aggregate liquidation preference (in dollars)	$ 75,492	$ 75,509
Preferred stock, dividend rate (as a percent)	7.875%	7.875%
7.125% Series C Preferred Stock
Preferred stock, shares authorized	3,400,000	3,400,000
Preferred stock, shares issued	3,400,000	3,400,000
Preferred stock, shares outstanding	3,400,000	3,400,000
Preferred stock, aggregate liquidation preference (in dollars)	$ 85,505	$ 85,522
Preferred stock, dividend rate (as a percent)	7.125%	7.125%