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Summary of Significant Accounting Policies - Changes in Product Warranty Accrual (Detail) - USD ($)
$ in Thousands
6 Months Ended
Jun. 30, 2018
Jul. 01, 2017
Movement in Standard and Extended Product Warranty Accrual, Increase (Decrease) [Roll Forward]    
Warranty accrual, beginning of period $ 1,149 $ 910
Accrual for warranties issued 643 606
Changes to pre-existing warranties (including changes in estimates) 551 (5)
Settlements made (502) (485)
Warranty accrual, end of period $ 1,841 $ 1,026