DEFERRED REVENUE - Rollforward of deferred revenue (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2018 USD ($)
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	$ 4,000
Current deferred revenue, Additions	12,926
Current deferred revenue, Less revenue recognized	12,236
Current deferred revenue, ending balance	10,778
Noncurrent deferred revenue, beginning balance	12,707
Noncurrent deferred revenue, Additions	8,405
Noncurrent deferred revenue, Less reclassification to current deferred revenue	5,814
Noncurrent deferred revenue, ending balance	38,119
Accounting Standard Update 2014-09
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	10,088
Noncurrent deferred revenue, beginning balance	35,528
Accounting Standard Update 2014-09 | Effect of Change Increase / (Decrease)
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	6,088
Noncurrent deferred revenue, beginning balance	22,821
Utica Shale
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	0
Current deferred revenue, Additions	9
Current deferred revenue, Less revenue recognized	9
Current deferred revenue, ending balance	18
Noncurrent deferred revenue, beginning balance	0
Noncurrent deferred revenue, Additions	0
Noncurrent deferred revenue, Less reclassification to current deferred revenue	9
Noncurrent deferred revenue, ending balance	30
Utica Shale | Accounting Standard Update 2014-09
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	18
Noncurrent deferred revenue, beginning balance	39
Utica Shale | Accounting Standard Update 2014-09 | Effect of Change Increase / (Decrease)
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	18
Noncurrent deferred revenue, beginning balance	39
Williston Basin
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	0
Current deferred revenue, Additions	1,088
Current deferred revenue, Less revenue recognized	643
Current deferred revenue, ending balance	1,462
Noncurrent deferred revenue, beginning balance	0
Noncurrent deferred revenue, Additions	1,622
Noncurrent deferred revenue, Less reclassification to current deferred revenue	1,017
Noncurrent deferred revenue, ending balance	4,820
Williston Basin | Accounting Standard Update 2014-09
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	1,017
Noncurrent deferred revenue, beginning balance	4,215
Williston Basin | Accounting Standard Update 2014-09 | Effect of Change Increase / (Decrease)
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	1,017
Noncurrent deferred revenue, beginning balance	4,215
Piceance/DJ Basins
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	4,000
Current deferred revenue, Additions	10,996
Current deferred revenue, Less revenue recognized	10,762
Current deferred revenue, ending balance	7,630
Noncurrent deferred revenue, beginning balance	12,707
Noncurrent deferred revenue, Additions	5,200
Noncurrent deferred revenue, Less reclassification to current deferred revenue	3,955
Noncurrent deferred revenue, ending balance	23,969
Piceance/DJ Basins | Accounting Standard Update 2014-09
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	7,396
Noncurrent deferred revenue, beginning balance	22,724
Piceance/DJ Basins | Accounting Standard Update 2014-09 | Effect of Change Increase / (Decrease)
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	3,396
Noncurrent deferred revenue, beginning balance	10,017
Barnett Shale
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	0
Current deferred revenue, Additions	814
Current deferred revenue, Less revenue recognized	803
Current deferred revenue, ending balance	1,630
Noncurrent deferred revenue, beginning balance	0
Noncurrent deferred revenue, Additions	1,583
Noncurrent deferred revenue, Less reclassification to current deferred revenue	814
Noncurrent deferred revenue, ending balance	8,986
Barnett Shale | Accounting Standard Update 2014-09
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	1,619
Noncurrent deferred revenue, beginning balance	8,217
Barnett Shale | Accounting Standard Update 2014-09 | Effect of Change Increase / (Decrease)
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	1,619
Noncurrent deferred revenue, beginning balance	8,217
Marcellus Shale
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	0
Current deferred revenue, Additions	19
Current deferred revenue, Less revenue recognized	19
Current deferred revenue, ending balance	38
Noncurrent deferred revenue, beginning balance	0
Noncurrent deferred revenue, Additions	0
Noncurrent deferred revenue, Less reclassification to current deferred revenue	19
Noncurrent deferred revenue, ending balance	314
Marcellus Shale | Accounting Standard Update 2014-09
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	38
Noncurrent deferred revenue, beginning balance	333
Marcellus Shale | Accounting Standard Update 2014-09 | Effect of Change Increase / (Decrease)
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	38
Noncurrent deferred revenue, beginning balance	$ 333