Net Income Per Common Share - Calculation of Diluted Net Income Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Numerator for diluted net (loss) income per share:
Net income (loss)	$ (16,645)	$ (3,919)	$ 61,314	$ (71,901)	$ (61,833)
Less: Series B preferred stock dividends	4,500	4,500	13,500	13,248
Less: undistributed earnings attributed to participating securities (diluted calculation)			26,241
Diluted net (loss) income attributable to common stockholders	$ (21,145)	$ (8,419)	$ 21,573	$ (85,149)
Denominator for diluted net (loss) income per share:
Weighted-average shares outstanding	206,380,800	206,168,035	206,261,993	204,307,431
Weighted-average unvested restricted shares outstanding	(4,039,591)	(4,197,396)	(4,014,718)	(2,636,314)
Effect of dilutive potential shares			35,327,739
Denominator for diluted net (loss) income per share	202,341,209	201,970,639	237,575,014	201,671,117
Diluted net (loss) income per share attributable to common stockholders	$ (0.10)	$ (0.04)	$ 0.09	$ (0.42)