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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

- Definition

Amount of unrealized gain on investment in debt security measured at fair value with change in fair value recognized in net income (trading).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 9
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27357-111563

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- Definition

Amount of unrealized loss on investment in debt security measured at fair value with change in fair value recognized in net income (trading).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 9
-Subparagraph (e)
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Amount of investment in debt security measured at fair value with change in fair value recognized in net income (trading).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121553693&loc=d3e26610-111562

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