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Commitments and Contingencies - Summary of Warranty Accrual Included in Accrued Liabilities (Detail) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Commitments and Contingencies Disclosure [Abstract]      
Balance at beginning of period $ 4,862 $ 3,913 $ 4,242
Accrual for current period warranties 5,117 5,482 5,378
Balance assumed from TVN acquisition 0 1,012 0
Warranty costs incurred (5,598) (5,545) (5,707)
Balance at end of period $ 4,381 $ 4,862 $ 3,913