DEFERRED REVENUE - Rollforward of deferred revenue (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2018 USD ($)
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue, beginning balance	$ 4,000
Current deferred revenue, Additions	19,526
Current deferred revenue, Less revenue recognized	18,462
Current deferred revenue, ending balance	11,152
Noncurrent deferred revenue, beginning balance	12,707
Noncurrent deferred revenue, Additions	13,188
Noncurrent deferred revenue, Less reclassification to current deferred revenue	9,092
Noncurrent deferred revenue, ending balance	39,624
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	14
Current deferred revenue, Less revenue recognized	14
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	14
Noncurrent deferred revenue, ending balance	25
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	1,367
Current deferred revenue, Less revenue recognized	985
Current deferred revenue, ending balance	1,399
Noncurrent deferred revenue, beginning balance	0
Noncurrent deferred revenue, Additions	1,851
Noncurrent deferred revenue, Less reclassification to current deferred revenue	1,296
Noncurrent deferred revenue, ending balance	4,770
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	16,846
Current deferred revenue, Less revenue recognized	16,186
Current deferred revenue, ending balance	8,056
Noncurrent deferred revenue, beginning balance	12,707
Noncurrent deferred revenue, Additions	9,014
Noncurrent deferred revenue, Less reclassification to current deferred revenue	6,483
Noncurrent deferred revenue, ending balance	25,255
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	1,236
Current deferred revenue, Less revenue recognized	1,214
Current deferred revenue, ending balance	1,641
Noncurrent deferred revenue, beginning balance	0
Noncurrent deferred revenue, Additions	2,323
Noncurrent deferred revenue, Less reclassification to current deferred revenue	1,236
Noncurrent deferred revenue, ending balance	9,304
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	63
Current deferred revenue, Less revenue recognized	63
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	63
Noncurrent deferred revenue, ending balance	270
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