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Fair Value Measurements - Narrative (Details) - USD ($) | 12 Months Ended |
--- | --- | ---
May 31, 2016 | Feb. 28, 2017
Fair value on a recurring basis |  |
Marketable securities | $ 70,405,000 | $ 0
Contractual maturities (less than) | 1 year |
Canadian treasury securities |  |
Fair value on a recurring basis |  |
Amortized cost basis of marketable securities | $ 70,400,000 |

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