ASSET RETIREMENT OBLIGATIONS (Narrative) (Details)	12 Months Ended
Dec. 31, 2017 USD ($) a property	Dec. 31, 2016 USD ($)
Reclamation activities	$ 21,477,000	$ 17,114,000
California [Member]
Reclamation activities	$ 11,578,000	$ 12,602,000
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