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Estimated Useful Lives of Property and Equipment (Detail)
12 Months Ended
Dec. 31, 2017
Property | Minimum  
Property, Plant and Equipment [Line Items]  
Property and equipment, estimated useful life 25 years
Property | Maximum  
Property, Plant and Equipment [Line Items]  
Property and equipment, estimated useful life 46 years
Leasehold improvements  
Property, Plant and Equipment [Line Items]  
Property and equipment, estimated useful life Over the shorter of lease term or the estimated useful lives of the assets
Optical Fibers | Minimum  
Property, Plant and Equipment [Line Items]  
Property and equipment, estimated useful life 10 years
Optical Fibers | Maximum  
Property, Plant and Equipment [Line Items]  
Property and equipment, estimated useful life 20 years
Computer and network equipment | Minimum  
Property, Plant and Equipment [Line Items]  
Property and equipment, estimated useful life 1 year
Computer and network equipment | Maximum  
Property, Plant and Equipment [Line Items]  
Property and equipment, estimated useful life 10 years
Office equipment | Minimum  
Property, Plant and Equipment [Line Items]  
Property and equipment, estimated useful life 1 year
Office equipment | Maximum  
Property, Plant and Equipment [Line Items]  
Property and equipment, estimated useful life 8 years
Motor vehicles | Minimum  
Property, Plant and Equipment [Line Items]  
Property and equipment, estimated useful life 4 years
Motor vehicles | Maximum  
Property, Plant and Equipment [Line Items]  
Property and equipment, estimated useful life 8 years