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Marketable Securities (Tables) | 9 Months Ended
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Sep. 30, 2017
Marketable Securities [Abstract] |
Amortized Cost And Fair Value Of Marketable Securities |
﻿ |  |  |  |  |  |  |  |  |  |  |  |  |
﻿As of September 30, 2017 |  |  | Amortized Cost |  |  | Gross Unrealized Gains |  |  | Gross Unrealized Losses |  |  | Fair Value |
﻿ |  |  |  |  |  |  |  |  |  |  |  |  |
﻿Corporate bonds |  | $ | 139,533 |  | $ | 129 |  | $ | (31) |  | $ | 139,631 |
﻿Certificates of deposit |  |  | 60,473 |  |  | - |  |  | - |  |  | 60,473 |
﻿Commercial paper |  |  | 24,234 |  |  | - |  |  | - |  |  | 24,234 |
﻿Asset backed securities |  |  | 22,476 |  |  | 11 |  |  | (6) |  |  | 22,481 |
﻿U.S. government bonds |  |  | 16,282 |  |  | 11 |  |  | (7) |  |  | 16,286 |
﻿Treasury bills |  |  | 10,992 |  |  | 1 |  |  | - |  |  | 10,993 |
﻿Agency bonds |  |  | 10,989 |  |  | 11 |  |  | (13) |  |  | 10,987 |
﻿Total marketable securities |  | $ | 284,979 |  | $ | 163 |  | $ | (57) |  | $ | 285,085 |
﻿ |  |  |  |  |  |  |  |  |  |  |  |  |
﻿As of December 31, 2016 |  |  | Amortized Cost |  |  | Gross Unrealized Gains |  |  | Gross Unrealized Losses |  |  | Fair Value |
﻿ |  |  |  |  |  |  |  |  |  |  |  |  |
﻿Corporate bonds |  | $ | 130,833 |  | $ | 40 |  | $ | (102) |  | $ | 130,771 |
﻿Certificates of deposit |  |  | 40,400 |  |  | - |  |  | - |  |  | 40,400 |
﻿Asset backed securities |  |  | 27,290 |  |  | 25 |  |  | - |  |  | 27,315 |
﻿Commercial paper |  |  | 20,228 |  |  | - |  |  | - |  |  | 20,228 |
﻿U.S. government bonds |  |  | 12,244 |  |  | 1 |  |  | (14) |  |  | 12,231 |
﻿Agency bonds |  |  | 4,600 |  |  | 4 |  |  | - |  |  | 4,604 |
﻿Municipal bonds |  |  | 1,400 |  |  | - |  |  | - |  |  | 1,400 |
﻿Total marketable securities |  | $ | 236,995 |  | $ | 70 |  | $ | (116) |  | $ | 236,949 |
﻿
Contractual Maturities Of Marketable Securities |
﻿ |  |  |  |  |  |  |
﻿As of September 30, 2017 |  |  | Amortized Cost |  |  | Fair Value |
﻿ |  |  |  |  |  |  |
﻿Due in one year or less |  | $ | 180,221 |  | $ | 180,236 |
﻿Due after one year through three years |  |  | 104,758 |  |  | 104,849 |
﻿ |  | $ | 284,979 |  | $ | 285,085 |
﻿

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- Definition Tabular disclosure of maturities of an entity's investments as well as any other information pertinent to the investments. + References No definition available. + Details
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- Definition Tabular disclosure of the reconciliation of available-for-sale securities from cost basis to fair value. + References No definition available. + Details
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