CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified			6 Months Ended	12 Months Ended	6 Months Ended	12 Months Ended	6 Months Ended
	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2013 9.25% Series A Preferred Stock	Dec. 31, 2012 9.25% Series A Preferred Stock	Jun. 30, 2013 7.875% Series B Preferred Stock	Dec. 31, 2012 7.875% Series B Preferred Stock	Jun. 30, 2013 7.125% Series C Preferred Stock
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized	100,000,000	100,000,000
Preferred stock, shares issued			2,000,000	2,000,000	3,000,000	3,000,000	3,400,000
Preferred stock, shares outstanding			2,000,000	2,000,000	3,000,000	3,000,000	3,400,000
Preferred stock, liquidation preference (in dollars)			$ 50,385	$ 50,393	$ 75,492	$ 75,324	$ 85,505
Preferred stock, dividend rate (as a percent)			9.25%	9.25%	7.875%	7.875%	7.125%
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	450,000,000	450,000,000
Common stock, issued	65,962,537	46,159,652
Common stock, outstanding	65,962,537	46,159,652