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Investments (Tables) | 12 Months Ended
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Dec. 31, 2017
Investments [Abstract] |
Summary of Short-term Investments | Investments as of December 31, 2017 consisted of the following: ﻿ ﻿
﻿ |  |  |  |  |  |  |  |  |
﻿ |  |  |  |  |  |  |  |  |
﻿ |  |  |  |  | Unrealized |  |  |
﻿ |  |  |  |  | Gains |  |  |
﻿ |  | Cost Basis |  | (Losses) |  | Fair Value
﻿Corporate bonds |  | $ | 2,925 |  | $ | (5) |  | $ | 2,920
﻿U.S. government agencies and securities |  |  | 3,000 |  |  | (1) |  |  | 2,999
﻿Commercial paper |  |  | 6,723 |  |  | — |  |  | 6,723
﻿Total |  | $ | 12,648 |  | $ | (6) |  | $ | 12,642
﻿ Investments as of December 31, 2016 consisted of the following: ﻿ ﻿
﻿ |  |  |  |  |  |  |  |  |
﻿ |  |  |  |  |  |  |  |  |
﻿ |  |  |  |  | Unrealized |  |  |
﻿ |  |  |  |  | Gains |  |  |
﻿ |  | Cost Basis |  | (Losses) |  | Fair Value
﻿Corporate bonds |  | $ | 8,284 |  | $ | (8) |  | $ | 8,276
﻿U.S. government agencies and securities |  |  | 8,542 |  |  | (13) |  |  | 8,529
﻿Commercial paper |  |  | 5,996 |  |  | — |  |  | 5,996
﻿Total |  | $ | 22,822 |  | $ | (21) |  | $ | 22,801
﻿

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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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