ASSET RETIREMENT OBLIGATIONS (Narrative) (Details) $ in Thousands	3 Months Ended
Mar. 31, 2018 USD ($) a property	Mar. 31, 2017 USD ($)
Reclamation activities	$ 6,021	$ 4,865
California [Member]
Reclamation activities	$ 4,402	$ 1,899
Adjacent aggregates sites \| property	2
Property, acres \| a	90

Amount of asset retirement obligations settled, or otherwise disposed of, during the period. This may include asset retirement obligations transferred to third parties associated with the sale of a long-lived asset.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849

Name:	us-gaap_AssetRetirementObligationLiabilitiesSettled
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration