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CASH, CASH EQUIVALENTS AND INVESTMENTS - Additional Information (Details) - USD ($) $ in Millions | Dec. 31, 2017 | Dec. 31, 2016
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Corporate Bonds [Member] |  |
Cash and Cash Equivalents [Line Items] |  |
Cash equivalents | $ 17.9 | $ 15.0
U.S. Government Bonds [Member] |  |
Cash and Cash Equivalents [Line Items] |  |
Cash equivalents | $ 0.0 | $ 30.0

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Definition Amount of 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. Excludes cash and cash equivalents within disposal group and discontinued operation. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.1) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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