DERIVATIVES - DERIVATIVE LOSS (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Components of the derivative loss
Total derivative loss	$ (36,544)	$ (8,742)
Commodity derivative
Components of the derivative loss
Derivative cash settlement gain (loss)	936	(4,312)
Change in fair value liability	(37,480)	(4,430)
Total derivative loss	(36,544)	(8,742)
Commodity derivative | Oil contracts
Components of the derivative loss
Derivative cash settlement gain (loss)	2,078	(4,506)
Commodity derivative | Gas contracts
Components of the derivative loss
Derivative cash settlement gain (loss)	$ (1,142)	$ 194