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Components of marketable securities (Details)
$ in Thousands
12 Months Ended
May 31, 2020
USD ($)
Marketable Securities [Line Items]  
Amortized Cost $ 276,850
Unrealized gains 577
Unrealized Losses (23)
Fair Value 277,404
US Treasury Securities [Member]  
Marketable Securities [Line Items]  
Amortized Cost 2,502
Unrealized gains 30
Fair Value 2,532
Commercial PaperAnd Corporate Bonds [Member]  
Marketable Securities [Line Items]  
Amortized Cost 257,700
Unrealized gains 347
Unrealized Losses (23)
Fair Value 258,024
Certificates of Deposit [Member]  
Marketable Securities [Line Items]  
Amortized Cost 16,648
Unrealized gains 200
Fair Value $ 16,848