Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2013	Jun. 30, 2015
Common Stock
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	150,000,000	150,000,000
Common stock, shares issued	86,259,684	92,258,690
Common stock, shares outstanding	86,259,684	92,258,690
Preferred Stock [Member]
Preferred stock, shares authorized	30,000,000	30,000,000
Preferred stock, par value	$ 0.01	$ 0.01
Series G Cumulative Redeemable Preferred Stock
Preferred stock, shares authorized	4,600,000	4,600,000
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock dividend rate (percentage)	6.875%
Preferred stock liquidation preference	$ 100,000	$ 100,000
Series H Cumulative Redeemable Preferred Stock
Preferred stock, shares authorized	4,000,000	4,000,000
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock dividend rate (percentage)	6.375%
Preferred stock liquidation preference	$ 100,000	$ 100,000