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MARKETABLE SECURITITES Marketable Securities (Details) - USD ($) $ in Thousands | Mar. 31, 2019 | Dec. 31, 2018
--- | --- | ---
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | $ 92,833 | $ 94,717
Gross Unrealized Gains | 137 | 2
Gross Unrealized Losses | (69) | (268)
Estimated Fair Market Value | 92,901 | 94,451
Investments due in 3 months or less: |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 12,635 | 6,788
Gross Unrealized Gains | 0 | 0
Gross Unrealized Losses | (9) | (2)
Estimated Fair Market Value | 12,626 | 6,786
Investments due in 4-12 months: |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 60,573 | 60,123
Gross Unrealized Gains | 53 | 0
Gross Unrealized Losses | (60) | (244)
Estimated Fair Market Value | 60,566 | 59,879
Investments due in 12 months or greater: |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 19,625 | 27,806
Gross Unrealized Gains | 84 | 2
Gross Unrealized Losses | 0 | (22)
Estimated Fair Market Value | 19,709 | 27,786
Corporate securities | Investments due in 3 months or less: |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 12,635 | 6,788
Gross Unrealized Gains | 0 | 0
Gross Unrealized Losses | (9) | (2)
Estimated Fair Market Value | 12,626 | 6,786
Corporate securities | Investments due in 4-12 months: |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 60,573 | 60,123
Gross Unrealized Gains | 53 | 0
Gross Unrealized Losses | (60) | (244)
Estimated Fair Market Value | 60,566 | 59,879
Corporate securities | Investments due in 12 months or greater: |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 19,625 | 27,806
Gross Unrealized Gains | 84 | 2
Gross Unrealized Losses | 0 | (22)
Estimated Fair Market Value | $ 19,709 | $ 27,786

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