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Share-based Payment Arrangements - Summary of Fair Value using Trinomial Tree Model and Inputs (Detail)
 12 Months Ended
Dec. 31, 2020
Years
¥ / shares
Dec. 31, 2019
Years
¥ / shares
Trinomial Tree Model [member] | USISH stock option plan [Member]    
Disclosure of terms and conditions of share-based payment arrangement [Line Items]    
Share price at the grant date   ¥ 15.84
Exercise price   13.34
Trinomial Tree Model [member] | USISH two thousand and twenty share options plan [Member]    
Disclosure of terms and conditions of share-based payment arrangement [Line Items]    
Share price at the grant date ¥ 21.55  
Exercise price 21.65  
Binomial Method [Member] | USISH core employees stock ownership plan restricted shares amended in 2020 [Member]    
Disclosure of terms and conditions of share-based payment arrangement [Line Items]    
Share price at the grant date   16.60
Exercise price   ¥ 13.34
Expected volatility   57.21%
Lock-up periods | Years   1
Risk free interest rate   1.55%
Binomial Method [Member] | USISH core employees stock ownership plan [Member]    
Disclosure of terms and conditions of share-based payment arrangement [Line Items]    
Share price at the grant date   ¥ 16.30
Exercise price   ¥ 13.34
Expected volatility   47.77%
Lock-up periods | Years   1
Risk free interest rate   2.70%
Binomial Method [Member] | USISH employee stock ownership restricted stock ownership plan amendment 2020 [Member]    
Disclosure of terms and conditions of share-based payment arrangement [Line Items]    
Share price at the grant date ¥ 24.30  
Expected volatility 56.97%  
Lock-up periods | Years 1.3  
Risk free interest rate 2.63%  
Bottom of range [member] | Trinomial Tree Model [member] | USISH stock option plan [Member]    
Disclosure of terms and conditions of share-based payment arrangement [Line Items]    
Expected volatility   45.07%
Expected lives | Years   3
Risk free interest rate   2.80%
Bottom of range [member] | Trinomial Tree Model [member] | USISH two thousand and twenty share options plan [Member]    
Disclosure of terms and conditions of share-based payment arrangement [Line Items]    
Expected volatility 48.14%  
Expected lives | Years 2.2  
Risk free interest rate 2.80%  
Top of range [member] | Trinomial Tree Model [member] | USISH stock option plan [Member]    
Disclosure of terms and conditions of share-based payment arrangement [Line Items]    
Expected volatility   51.80%
Expected lives | Years   5
Risk free interest rate   2.97%
Top of range [member] | Trinomial Tree Model [member] | USISH two thousand and twenty share options plan [Member]    
Disclosure of terms and conditions of share-based payment arrangement [Line Items]    
Expected volatility 53.57%  
Expected lives | Years 4.2  
Risk free interest rate 2.99%