NET INCOME (LOSS) PER SHARE - Calculation of Net Income (Loss) Per 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 (both basic and diluted)
Net income (loss) relevant to common stockholders									$ 12,613	$ (53,147)	$ (45,853)
Denominator
Denominator for basic income (loss) per share (in shares)	83,040	83,040	83,040	55,996	52,628	52,975	39,496	34,993	76,371	44,787	34,993
Denominator for diluted income (loss) per share (in shares)	86,818	86,264	86,279	55,996	52,628	52,975	39,496	34,993	79,583	44,787	34,993
Basic net income (loss) per common share (in dollars per share)	$ 0.12	$ 0.26	$ 0.06	$ (0.43)	$ (0.33)	$ (0.26)	$ (0.24)	$ (0.37)	$ 0.17	$ (1.19)	$ (1.31)
Diluted net income (loss) per common share (in dollars per share)	$ 0.12	$ 0.25	$ 0.06	$ (0.43)	$ (0.33)	$ (0.26)	$ (0.24)	$ (0.37)	$ 0.16	$ (1.19)	$ (1.31)
Stock options
Denominator
Dilutive effect of stock options/units (in shares)									2,903	0	0
Performance stock units
Denominator
Dilutive effect of stock options/units (in shares)									59	0	0
Restricted stock units
Denominator
Dilutive effect of stock options/units (in shares)									250	0	0