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Balance Sheet Details - Additional Information (Detail) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Organization Consolidation And Presentation Of Financial Statements [Abstract]      
Depreciation of property and equipment $ 1,236 $ 843 $ 647
Removal of fully depreciated property, machinery and equipment $ 400 $ 200 $ 100