Net Income Per Common Share- Calculation of Basic Net Income Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Numerator for basic net income (loss) per share:
Net income (loss)	$ 22,409	$ (73,483)	$ 77,959	$ (67,982)	$ (61,833)
Less: Series B preferred stock dividends	4,500	4,500	9,000	8,748
Less: undistributed earnings attributed to participating securities (basic calculation)	10,367		39,932
Basic net income (loss) attributable to common stockholders	$ 7,542	$ (77,983)	$ 29,027	$ (76,730)
Denominator for basic net income (loss) per share:
Weighted-average shares outstanding	206,235,839	204,368,982	206,201,937	203,361,710
Weighted-average unvested restricted shares outstanding	(3,894,630)	(2,481,891)	(4,002,144)	(1,842,836)
Denominator for basic net income (loss) per share:	202,341,209	201,887,091	202,199,793	201,518,874
Basic net income (loss) per share attributable to common stockholders	$ 0.04	$ (0.39)	$ 0.14	$ (0.38)