Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	6 Months Ended	12 Months Ended
	Jun. 30, 2013	Dec. 31, 2012
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized	12,000,000	12,000,000
Preferred stock, dividend rate (as a percent)	8.125%	8.125%
Preferred stock, Liquidation Preference (in dollars per share)	$ 25.00	$ 25.00
Preferred stock, Shares issued	4,400,000	4,400,000
Preferred stock, Shares outstanding	4,400,000	4,400,000
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	500,000,000	500,000,000
Common stock, Shares issued	99,626,000	89,366,000
Common stock, Shares outstanding	99,626,000	89,366,000
Additional paid-in capital, offering costs (in dollars)	$ 74,492	$ 70,238