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Intangible Assets - Additional Information (Detail) - USD ($)
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]      
Amortization expense $ 119,000 $ 130,000 $ 134,000
Patents [Member]      
Finite-Lived Intangible Assets [Line Items]      
Future amortization expense from patent assets held for 2019 108,000    
Future amortization expense from patent assets held for 2020 103,000    
Future amortization expense from patent assets held for 2021 93,000    
Future amortization expense from patent assets held for 2022 62,000    
Future amortization expense from patent assets held for 2023 $ 51,000