Share repurchase program (Tables)  | 
6 Months Ended | ||||||||||||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Jul. 31, 2021  | |||||||||||||||||||||||||||||||||||||||||||
| Share repurchase program | |||||||||||||||||||||||||||||||||||||||||||
| Summary of the Company's common stock repurchase activity | 
 A summary of common stock repurchase activity is presented in the following table: 
  | 
||||||||||||||||||||||||||||||||||||||||||
| X | ||||||||||
- Definition Tabular disclosure of the changes in outstanding nonvested shares. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
  | 
| X | ||||||||||
- References No definition available. 
  |