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Intangible Assets - Schedule of Patent Cost and Other Asset (Detail) - Patents [Member] - USD ($)
$ in Thousands
Dec. 31, 2018
Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]    
Patent costs $ 1,979 $ 2,093
Accumulated amortization (1,380) (1,386)
Finite-lived intangible assets, net $ 599 $ 707