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Intangible Assets - Additional Information (Detail) - USD ($)
6 Months Ended 12 Months Ended
Jun. 30, 2019
Dec. 31, 2018
Goodwill And Intangible Assets Disclosure [Abstract]    
Impairment charge   $ 0
Subsequent impairment of the underlying assets $ 0  
Expected annual amortization expense for 2019 300,000  
Expected annual amortization expense for 2020 100,000  
Expected annual amortization expense for 2021 100,000  
Expected annual amortization expense for 2022 100,000  
Expected annual amortization expense for 2023 100,000  
Expected annual amortization expense for 2024 100,000  
Expected annual amortization expense for 2025 $ 100,000