Net Income Per Common Share - Calculation of Diluted 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 diluted 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 (diluted calculation)	27,993	669
Diluted net income attributable to common stockholders	$ 23,057	$ 584
Denominator for diluted 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)
Effect of dilutive potential shares	35,941,341	35,362,132
Denominator for diluted net income per share:	237,999,718	236,508,697
Diluted net income per share attributable to common stockholders	$ 0.10	$ 0.00