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Investments - Additional Information (Detail) - USD ($)
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Currency risk [member]    
Disclosure of detailed information about investment property [line items]    
Risk exposure associated with instruments $ 0  
Other price risk [member]    
Disclosure of detailed information about investment property [line items]    
Risk exposure associated with instruments $ 0  
Bottom of range [member] | Time deposits denominated with a contractual maturity of less than 365 days [member]    
Disclosure of detailed information about investment property [line items]    
Interest rates on time deposits 0.27% 2.00%
Bottom of range [member] | Time deposits with a contractual maturity of more than 365 days [member]    
Disclosure of detailed information about investment property [line items]    
Interest rates on time deposits 1.20% 3.25%
Top of range [member] | Time deposits denominated with a contractual maturity of less than 365 days [member]    
Disclosure of detailed information about investment property [line items]    
Interest rates on time deposits 4.38% 3.75%
Top of range [member] | Time deposits with a contractual maturity of more than 365 days [member]    
Disclosure of detailed information about investment property [line items]    
Interest rates on time deposits 4.25% 4.38%
Bottom of range Bonds with semiannual interest payment [member]    
Disclosure of detailed information about investment property [line items]    
Semiannual interest payment, interest rates 0.21% 2.06%
Top of range Bonds with semiannual interest payment [member]    
Disclosure of detailed information about investment property [line items]    
Semiannual interest payment, interest rates 3.32% 3.32%