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FAIR VALUE MEASUREMENTS - SECURITY TYPE (Details) - USD ($) $ in Thousands | Dec. 31, 2015 | Dec. 31, 2014
--- | --- | ---
Included in cash and cash equivalents |  |
Amortized Cost | $ 19,177 | $ 40,342
Gross Unrealized Losses | (1) |
Estimated Fair Value | 19,176 | 40,342
Restricted cash |  |
Amortized Cost | 267 | 266
Estimated Fair Value | 267 | 266
Marketable securities |  |
Amortized Cost | 125,397 | 127,661
Gross Unrealized Gains | 50 | 16
Gross Unrealized Losses | (262) | (100)
Estimated Fair Value | 125,185 | 127,577
Money market funds |  |
Included in cash and cash equivalents |  |
Amortized Cost | 4,577 | 40,342
Estimated Fair Value | 4,577 | 40,342
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 | 267 | 266
Estimated Fair Value | 267 | 266
Government-sponsored enterprise securities (due in less than 1 year) |  |
Marketable securities |  |
Amortized Cost |  | 401
Gross Unrealized Losses |  | (1)
Estimated Fair Value |  | 400
Government-sponsored enterprise securities (due in 1 to 2 years) |  |
Marketable securities |  |
Amortized Cost | 10,007 | 6,556
Gross Unrealized Losses | (57) | (7)
Estimated Fair Value | 9,950 | 6,549
Commercial paper (due in less than 1 year) |  |
Marketable securities |  |
Amortized Cost | 27,661 | 10,985
Gross Unrealized Gains | 49 | 14
Gross Unrealized Losses | (2) |
Estimated Fair Value | 27,708 | 10,999
Corporate notes (due in less than 1 year) |  |
Marketable securities |  |
Amortized Cost | 64,892 | 97,307
Gross Unrealized Gains | 1 | 2
Gross Unrealized Losses | (77) | (63)
Estimated Fair Value | 64,816 | 97,246
Corporate notes (due in 1 to 2 years) |  |
Marketable securities |  |
Amortized Cost | 22,837 | 12,412
Gross Unrealized Losses | (126) | (29)
Estimated Fair Value | $ 22,711 | $ 12,383

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