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Fair Value Measurements - Additional Information (Detail) - USD ($)
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Transfer of Liabilities, amount $ 0 $ 0
Transfer of assets, amount $ 0 0
Maximum    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Cash and cash equivalent maturity period 90 days  
Maximum | Short-term Loans    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Term of loan 12 months  
Maximum | Line of Credit Accounts    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Term of loan 12 months  
Maximum | Installment Loans and RPAs    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Term of loan 60 months  
Maximum | RPAs    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Estimated delivery term 18 months  
Minimum | Installment Loans and RPAs    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Term of loan 2 months  
Minimum | RPAs    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Estimated delivery term 6 months  
Fair Value Measurements Nonrecurring Member    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Assets fair value non-recurring $ 0 0
Liabilities fair value non-recurring $ 0 $ 0