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Marketable Securities (Tables) | 6 Months Ended
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Nov. 30, 2015
Investments, Debt and Equity Securities [Abstract] |
Marketable Securities | As of November 30, 2015 and May 31, 2015, marketable securities consisted of the following (in thousands of dollars):
As of November 30, 2015 | Amortized cost |  | Gross Unrealized Gains |  | Gross Unrealized Losses |  | Fair Value
Available-for-sale securities |  |  |  |  |  |  |
U.S. government agency obligations | $ | 1,800 |  |  | $ | — |  |  | $ | (161 | ) |  | $ | 1,639 |
| $ | 1,800 |  |  | $ | — |  |  | $ | (161 | ) |  | $ | 1,639 |
As of May 31, 2015 | Amortized cost |  | Gross Unrealized Gains |  | Gross Unrealized Losses |  | Fair Value
Available-for-sale securities |  |  |  |  |  |  |
U.S. government agency obligations | $ | 1,825 |  |  | $ | — |  |  | $ | (136 | ) |  | $ | 1,689 |
| $ | 1,825 |  |  | $ | — |  |  | $ | (136 | ) |  | $ | 1,689 |

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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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