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FAIR VALUE MEASUREMENTS - SECURITY TYPE (Details) - USD ($) $ in Thousands | Dec. 31, 2016 | Dec. 31, 2015
--- | --- | ---
Included in cash and cash equivalents: |  |
Amortized Cost | $ 11,193 | $ 19,177
Gross Unrealized Losses |  | (1)
Estimated Fair Value | 11,193 | 19,176
Restricted cash: |  |
Amortized Cost | 268 | 267
Estimated Fair Value | 268 | 267
Marketable securities: |  |
Amortized Cost | 116,042 | 125,397
Gross Unrealized Gains | 54 | 50
Gross Unrealized Losses | (107) | (262)
Estimated Fair Value | 115,989 | 125,185
Money market funds |  |
Included in cash and cash equivalents: |  |
Amortized Cost | 11,193 | 4,577
Estimated Fair Value | 11,193 | 4,577
Commercial paper |  |
Included in cash and cash equivalents: |  |
Amortized Cost |  | 7,599
Estimated Fair Value |  | 7,599
Government-sponsored enterprise securities |  |
Included in cash and cash equivalents: |  |
Amortized Cost |  | 1,999
Estimated Fair Value |  | 1,999
Corporate notes |  |
Included in cash and cash equivalents: |  |
Amortized Cost |  | 5,002
Gross Unrealized Losses |  | (1)
Estimated Fair Value |  | 5,001
Certificate of deposit |  |
Restricted cash: |  |
Amortized Cost | 268 | 267
Estimated Fair Value | 268 | 267
Government-sponsored enterprise securities (due in less than one year) |  |
Marketable securities: |  |
Amortized Cost | 5,000 |
Gross Unrealized Losses | (3) |
Estimated Fair Value | 4,997 |
Government-sponsored enterprise securities (due in one to two years) |  |
Marketable securities: |  |
Amortized Cost | 12,500 | 10,007
Gross Unrealized Losses | (42) | (57)
Estimated Fair Value | 12,458 | 9,950
Commercial paper (due in less than one year) |  |
Marketable securities: |  |
Amortized Cost | 31,024 | 27,661
Gross Unrealized Gains | 50 | 49
Gross Unrealized Losses | (5) | (2)
Estimated Fair Value | 31,069 | 27,708
Corporate notes (due in less than one year) |  |
Marketable securities: |  |
Amortized Cost | 66,012 | 64,892
Gross Unrealized Gains | 4 | 1
Gross Unrealized Losses | (47) | (77)
Estimated Fair Value | 65,969 | 64,816
Corporate notes (due in one to two years) |  |
Marketable securities: |  |
Amortized Cost | 1,506 | 22,837
Gross Unrealized Losses | (10) | (126)
Estimated Fair Value | $ 1,496 | $ 22,711

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