DERIVATIVE INSTRUMENTS - (Gain) Loss on Derivative Instruments (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Derivative [Line Items]
Change in fair value of derivative instruments, net:	$ 14,169	$ (22,166)	$ (2,379)	$ (72,087)
Cash (receipts) payments on derivative instruments, net:	7,530	(343)	19,919	5,717
Loss (gain) on derivative instruments, net	21,699	(22,509)	17,540	(66,370)
Gas contracts
Derivative [Line Items]
Change in fair value of derivative instruments, net:	14,566	(5,748)	2,777	(27,939)
Cash (receipts) payments on derivative instruments, net:	(9,918)	(1,308)	(15,037)	1,136
Oil contracts
Derivative [Line Items]
Change in fair value of derivative instruments, net:	(397)	(16,418)	(5,156)	(44,148)
Cash (receipts) payments on derivative instruments, net:	$ 17,448	$ 965	$ 34,956	$ 4,581