ASSET RETIREMENT OBLIGATION (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
ASSET RETIREMENT OBLIGATION
Asset retirement obligation current	$ 894	$ 708		$ 1,078
Collateralized with restricted cash	$ 3,750	$ 3,732	$ 3,668	$ 3,668

Amount of cash and cash equivalents restricted as to withdrawal or usage. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Balance Type:	debit
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