Net (Loss) Income Per Common Share- Calculation of Basic Net (Loss) Income Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Numerator for basic net (loss) income per share:
Net (loss) income	$ (21,324)	$ 22,409	$ (3,535)	$ 77,959	$ 201,700
Less: Series B preferred stock dividends	(4,500)	(4,500)	(9,000)	(9,000)
Less: undistributed earnings attributed to participating securities (basic calculation)		(10,367)		(39,932)
Basic net (loss) income attributable to common stockholders	$ (25,824)	$ 7,542	$ (12,535)	$ 29,027
Denominator for basic net (loss) income per share:
Weighted-average shares outstanding	206,490,690	206,235,839	206,436,048	206,201,937
Weighted-average unvested restricted shares outstanding	(3,857,807)	(3,894,630)	(3,907,045)	(4,002,144)
Denominator for basic net (loss) income per share	202,632,883	202,341,209	202,529,003	202,199,793
Basic net (loss) income per share attributable to common stockholders	$ (0.13)	$ 0.04	$ (0.06)	$ 0.14