(LOSS) / INCOME PER COMMON SHARE (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Numerator:
Net (loss) / income	$ (45,392)	$ (67,468)	$ (82,545)	$ 26,864	$ 5,804	$ (37,351)	$ 37,995	$ 60,858	$ (168,541)	$ 67,306	$ 129,569
Denominator:
Weighted-average shares outstanding, basic	83,083	82,989	82,979	82,960	82,776	82,682	82,681	82,680	83,003	82,705	62,779
Basic net (loss) / income per share (in dollars per share)	$ (0.55)	$ (0.81)	$ (0.99)	$ 0.32	$ 0.07	$ (0.45)	$ 0.46	$ 0.74	$ (2.03)	$ 0.81	$ 2.06
Numerator:
Net (loss) / income	$ (45,392)	$ (67,468)	$ (82,545)	$ 26,864	$ 5,804	$ (37,351)	$ 37,995	$ 60,858	$ (168,541)	$ 67,306	$ 129,569
Denominator:
Weighted-average shares outstanding, basic	83,083	82,989	82,979	82,960	82,776	82,682	82,681	82,680	83,003	82,705	62,779
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Weighted-average shares outstanding, diluted	83,083	82,989	82,979	82,991	82,776	82,682	82,681	82,680	83,003	82,705	63,113
Diluted net (loss) / income per share (in dollars per share):	$ (0.55)	$ (0.81)	$ (0.99)	$ 0.32	$ 0.07	$ (0.45)	$ 0.46	$ 0.74	$ (2.03)	$ 0.81	$ 2.05
RSU's
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Incremental common shares attributable to share-based payment arrangements											334