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OPERATING REVENUES - Revenue Recognition (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Disaggregation of operating revenue
Total oil, natural gas and natural gas liquids sales	$ 61,245		$ 165,652
Other	350	$ 363	613	$ 1,386
Total operating revenues	61,595	96,953	166,265	352,688
Calculated under Revenue Guidance in Effect before Topic 606
Disaggregation of operating revenue
Total oil, natural gas and natural gas liquids sales		96,590		351,302
Other		363		1,386
Total operating revenues		96,953		352,688
Oil
Disaggregation of operating revenue
Total oil, natural gas and natural gas liquids sales	53,918		145,743
Total operating revenues	53,918	88,256	145,743	319,472
Oil \| Calculated under Revenue Guidance in Effect before Topic 606
Disaggregation of operating revenue
Total oil, natural gas and natural gas liquids sales		88,256		319,472
Natural gas
Disaggregation of operating revenue
Total oil, natural gas and natural gas liquids sales	1,407		5,286
Total operating revenues	1,407	2,886	5,286	15,051
Natural gas \| Calculated under Revenue Guidance in Effect before Topic 606
Disaggregation of operating revenue
Total oil, natural gas and natural gas liquids sales		2,886		15,051
Natural gas liquids
Disaggregation of operating revenue
Total oil, natural gas and natural gas liquids sales	5,920		14,623
Total operating revenues	5,920	5,448	14,623	16,779
Natural gas liquids \| Calculated under Revenue Guidance in Effect before Topic 606
Disaggregation of operating revenue
Total oil, natural gas and natural gas liquids sales		$ 5,448		$ 16,779
Accounts receivable
Disaggregation of operating revenue
Due from contracts with customers	$ 37,100		$ 37,100		$ 24,100