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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Available-for-sale Investments) (Details) | Dec. 31, 2016 USD ($) | Dec. 31, 2015 USD ($) Securities
--- | --- | ---
Schedule of Available-for-sale Securities [Line Items] |  |
Weighted Average Interest Rate on Investments | 1.23% | 0.84%
Amortized cost | $ 188,543,000 | $ 83,866,000
Gross unrealized gains | 38,000 | 8,000
Gross unrealized loss | 258,000 | 105,000
Estimated fair market value | 188,323,000 | 83,769,000
Corporate securities |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized cost | 46,338,000 | 38,586,000
Gross unrealized gains | 2,000 | 7,000
Gross unrealized loss | 2,000 | 10,000
Estimated fair market value | 46,338,000 | 38,583,000
Investments due in 4-12 months: |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized cost | 78,900,000 | 33,654,000
Gross unrealized gains | 15,000 | 1,000
Gross unrealized loss | 76,000 | 36,000
Estimated fair market value | 78,839,000 | 33,619,000
Investments due between 12 months or greater: |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized cost | 63,305,000 | 11,626,000
Gross unrealized gains | 21,000 | 0
Gross unrealized loss | 180,000 | 59,000
Estimated fair market value | $ 63,146,000 | $ 11,567,000
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | 0 | 0
Commercial paper [Member] | Corporate securities |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized cost | $ 36,996,000 |
Gross unrealized gains | 0 |
Gross unrealized loss | 0 |
Estimated fair market value | 36,996,000 |
Commercial paper [Member] | Investments due in 4-12 months: |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized cost | 19,186,000 |
Gross unrealized gains | 0 |
Gross unrealized loss | 0 |
Estimated fair market value | 19,186,000 |
Corporate securities [Member] | Corporate securities |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized cost | 9,342,000 | $ 38,586,000
Gross unrealized gains | 2,000 | 7,000
Gross unrealized loss | 2,000 | 10,000
Estimated fair market value | 9,342,000 | 38,583,000
Corporate securities [Member] | Investments due in 4-12 months: |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized cost | 59,714,000 | 33,654,000
Gross unrealized gains | 15,000 | 1,000
Gross unrealized loss | 76,000 | 36,000
Estimated fair market value | 59,653,000 | 33,619,000
Corporate securities [Member] | Investments due between 12 months or greater: |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized cost | 63,305,000 | 11,626,000
Gross unrealized gains | 21,000 | 0
Gross unrealized loss | 180,000 | 59,000
Estimated fair market value | $ 63,146,000 | $ 11,567,000

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