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Share-based payment - Additional Information (Detail)
 12 Months Ended
Dec. 31, 2018
Disclosure of terms and conditions of share-based payment arrangement [line items]  
Percentage of stock split approved 0.50
Percentage of variable compensation paid in cash 50.00%
Percentage of variable compensation paid in shares 50.00%
Period of variable compensation paid in shares Three years
Options vesting period 5 years
Bottom of range [member]  
Disclosure of terms and conditions of share-based payment arrangement [line items]  
Options vesting period 1 year
Bottom of range [member] | Partner plan [member]  
Disclosure of terms and conditions of share-based payment arrangement [line items]  
Share-based payment arrangement options granted expiration period 3 years
Top of range [member]  
Disclosure of terms and conditions of share-based payment arrangement [line items]  
Percentage of shares held by controlling and minority stockholders 0.50%
Options vesting period 7 years
Top of range [member] | Partner plan [member]  
Disclosure of terms and conditions of share-based payment arrangement [line items]  
Share-based payment arrangement options granted expiration period 5 years