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Revenue - Additional Information (Detail)
3 Months Ended
Mar. 31, 2018
USD ($)
Revenue [Line Items]  
Period of assurance-based warranty for product defects 90 days to five years
Remaining performance obligations $ 0
Revenue recognized that was included in unearned revenue $ 3,500,000
Minimum [Member]  
Revenue [Line Items]  
Lessor sales type lease arrangement terms for network equipments 18 months
Maintenance service periods 1 month
Maximum [Member]  
Revenue [Line Items]  
Lessor sales type lease arrangement terms for network equipments 5 years
Maintenance service periods 5 years