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Components of marketable securities (Details) - USD ($) $ in Thousands | 9 Months Ended | 12 Months Ended
--- | --- | ---
Feb. 28, 2021 | May 31, 2020
Marketable Securities [Line Items] |  |
Amortized Cost | $ 279,884 | $ 276,850
Unrealized gains | 234 | 577
Unrealized Losses | (253) | (23)
Fair Value | 279,865 | 277,404
US Treasury Securities [Member] |  |
Marketable Securities [Line Items] |  |
Amortized Cost | 0 | 2,502
Unrealized gains | 0 | 30
Unrealized Losses | 0 |
Fair Value | 0 | 2,532
Commercial Paper And Corporate Bonds [Member] |  |
Marketable Securities [Line Items] |  |
Amortized Cost | 271,600 | 257,700
Unrealized gains | 185 | 347
Unrealized Losses | (253) | (23)
Fair Value | 271,532 | 258,024
Certificates of Deposit [Member] |  |
Marketable Securities [Line Items] |  |
Amortized Cost | 8,284 | 16,648
Unrealized gains | 49 | 200
Unrealized Losses | 0 |
Fair Value | $ 8,333 | $ 16,848

X
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