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Fair Value Measurements - Additional Information (Detail) - USD ($)
Sep. 30, 2019
Dec. 31, 2018
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Fair value, assets transfers from Level 1 to Level 2 measurement $ 0  
Fair value, assets transfers from Level 2 to Level 1 measurement 0  
Fair value of liabilities on recurring basis 0 $ 0
Restricted investments 1,400,000 1,400,000
Level 2 [Member] | Certificate of Deposit [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Restricted investments $ 1,400,000 $ 1,400,000