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ROYALTY EXPENSE (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2017 | Sep. 30, 2016 | Sep. 30, 2017 | Sep. 30, 2016
Other Income and Expenses [Abstract] |  |  |  |
Royalty expense | $ 2,596 | $ 2,285 | $ 7,739 | $ 6,688

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- References No definition available. + Details
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Data Type: | xbrli:stringItemType
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- Definition Amount of expense related to royalty payments under a contractual arrangement such as payment for mineral and drilling rights and use of technology or intellectual property. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.3) -URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688 + Details
Name: | us-gaap_RoyaltyExpense
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Balance Type: | debit
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