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Components of marketable securities (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Aug. 31, 2020	May 31, 2020
Marketable Securities [Line Items]
Amortized Cost	$ 305,624	$ 276,850
Unrealized gains	972	577
Unrealized Losses	(57)	(23)
Fair Value	306,539	277,404
US Treasury Securities [Member]
Marketable Securities [Line Items]
Amortized Cost	2,502	2,502
Unrealized gains	14	30
Fair Value	2,516	2,532
Commercial PaperAnd Corporate Bonds [Member]
Marketable Securities [Line Items]
Amortized Cost	286,211	257,700
Unrealized gains	820	347
Unrealized Losses	(57)	(23)
Fair Value	286,974	258,024
Certificates of Deposit [Member]
Marketable Securities [Line Items]
Amortized Cost	16,911	16,648
Unrealized gains	138	200
Fair Value	$ 17,049	$ 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=118939692&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)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27357-111563

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- Definition

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=118954083&loc=d3e26610-111562

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