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STATEMENTS OF CASH FLOWS DATA (Tables) | 12 Months Ended
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Dec. 31, 2017
Supplemental Cash Flow Elements [Abstract] |
Supplemental schedule of non-cash operating and investing activities |
|  | Year Ended December 31, |
|  | 2017 |  |  | 2016 |  |  | 2015 |
|  | (In thousands) |
Supplemental investing activities: |  |  |  |  |  |  |  |  |  |  |  |
Net unrealized (loss) gain on marketable securities |  | $ | (154 | ) |  | $ | 160 |  |  | $ | (129 | )

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- References No definition available. + Details
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