Fair value portion of guarantee, including, but not limited to, financial standby letter of credit, fair value guarantee, guarantee of collection of scheduled contractual cash flows from financial assets, and contracts that contingently require the guarantor to make payments or perform services.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 460
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82913245&loc=d3e12201-110248

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

COMMITMENTS AND CONTINGENT LIABILITIES - Narrative (Details) $ in Thousands			3 Months Ended
	Aug. 23, 2017 plaintiff	Apr. 24, 2017 plaintiff	Mar. 31, 2018 USD ($) mine	Dec. 31, 2017 USD ($)
Loss Contingencies [Line Items]
Number of mines sold \| mine			5
Fair value of guarantees \| $			$ 982	$ 1,040
Fitzwater Litigation \| Pending Litigation
Loss Contingencies [Line Items]
Number of plaintiffs		3
Casey Litigation \| Pending Litigation
Loss Contingencies [Line Items]
Number of plaintiffs	2