Summary of Significant Accounting Policies - Fair value of financial instruments (Details) - USD ($) $ in Thousands  | 
May 31, 2022  | 
May 31, 2021  | 
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| Level 1 | ||
| Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] | ||
| Assets fair value | $ 0 | $ 0 | 
| Liabilities fair value | 0 | 0 | 
| Level 2 | ||
| Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] | ||
| Assets fair value | 0 | 0 | 
| Liabilities fair value | 0 | 0 | 
| Level 3 | ||
| Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] | ||
| Assets fair value | 0 | 0 | 
| Liabilities fair value | $ 0 | $ 0 | 
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- Definition Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. No definition available. 
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- Definition Fair value of financial and nonfinancial obligations. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
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