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Financial Risk Management - Disclosure of Detailed Information About Hedging Instruments (Details)
$ in Thousands
 12 Months Ended
Jan. 31, 2020
NZD ($)
Integer
Jan. 31, 2019
NZD ($)
Integer
Jan. 31, 2018
NZD ($)
Integer
Statement Line Items [Line Items]      
Notional amount $ 19,700    
Buy USD / Sell NZD [Member] | Less than Six Months [Member]      
Statement Line Items [Line Items]      
Notional amount $ 34,395 $ 48,149
Average foreign exchange rate | Integer 0.6620 0.7061
Buy AUD / Sell NZD [Member] | Less than Six Months [Member]      
Statement Line Items [Line Items]      
Notional amount $ 2,247
Average foreign exchange rate | Integer 0.8900