Net Income Per Common Share- Calculation of Basic Net Income Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Numerator for basic net income per share:
Net income	$ 17,789	$ 55,550	$ 201,700
Less: Series B preferred stock dividends	(4,500)	(4,500)
Less: undistributed earnings attributed to participating securities (basic calculation)	(8,445)	(29,506)
Basic net income attributable to common stockholders	$ 4,844	$ 21,544
Denominator for basic net income per share:
Weighted-average shares outstanding	206,380,800	206,168,035
Weighted-average unvested restricted shares outstanding	(3,956,831)	(4,109,658)
Denominator for basic net income per share	202,423,969	202,058,377
Basic net income per share attributable to common stockholders	$ 0.02	$ 0.11