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Components of marketable securities (Details) - USD ($) $ in Thousands | 6 Months Ended | 12 Months Ended
--- | --- | ---
Nov. 30, 2020 | May 31, 2020
Marketable Securities [Line Items] |  |
Amortized Cost | $ 276,625 | $ 276,850
Unrealized gains | 424 | 577
Unrealized Losses | (151) | (23)
Fair Value | 276,898 | 277,404
US Treasury Securities [Member] |  |
Marketable Securities [Line Items] |  |
Amortized Cost |  | 2,502
Unrealized gains |  | 30
Fair Value |  | 2,532
Commercial Paper And Corporate Bonds [Member] |  |
Marketable Securities [Line Items] |  |
Amortized Cost | 264,616 | 257,700
Unrealized gains | 338 | 347
Unrealized Losses | (151) | (23)
Fair Value | 264,803 | 258,024
Certificates of Deposit [Member] |  |
Marketable Securities [Line Items] |  |
Amortized Cost | 12,009 | 16,648
Unrealized gains | 86 | 200
Fair Value | $ 12,095 | $ 16,848

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