GOODWILL - Schedule of goodwill (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Goodwill [Line Items]
Accumulated goodwill impairment	$ 303,050	$ 303,050	$ 303,050
Piceance/DJ Basins
Goodwill [Line Items]
Accumulated goodwill impairment	45,478	45,478	45,478
Williston Basin
Goodwill [Line Items]
Accumulated goodwill impairment	$ 257,572	$ 257,572	$ 257,572

Amount of accumulated impairment loss for an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a,h)
-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

Name:	us-gaap_GoodwillImpairedAccumulatedImpairmentLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant