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, 2016	Mar. 31, 2015	Dec. 31, 2015
Numerator for basic net income per share:
Net income	$ 55,550	$ 5,501	$ (61,833)
Less: Series B preferred stock dividends	4,500	4,248
Less: undistributed earnings attributed to participating securities (basic calculation)	29,506	705
Basic net income attributable to common stockholders	$ 21,544	$ 548
Denominator for basic net income per share:
Weighted-average shares outstanding	206,168,035	202,343,245
Weighted-average unvested restricted shares outstanding	(4,109,658)	(1,196,680)
Denominator for basic net income per share:	202,058,377	201,146,565
Basic net income per share attributable to common stockholders	$ 0.11	$ 0.00