Fair value (Details) - Recurring - Marketable equity securities $ in Thousands |
Apr. 30, 2019
USD ($)
|
|---|---|
| Level 1 | |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | |
| Other investments | $ 77,356 |
| Level 2 | |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | |
| Other investments | 0 |
| Level 3 | |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | |
| Other investments | $ 0 |