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Composition of Certain Balance Sheet Accounts - Property and Equipment (Detail) - USD ($)
$ in Thousands
Mar. 31, 2018
Dec. 31, 2017
Property, Plant and Equipment [Line Items]    
Property and equipment, gross $ 882,703 $ 1,053,923
Accumulated depreciation (352,016) (397,885)
Property and equipment, net 530,687 656,038
Office Equipment, Furniture, Fixtures and Other [Member]    
Property, Plant and Equipment [Line Items]    
Property and equipment, gross 47,849 46,445
Leasehold Improvements [Member]    
Property, Plant and Equipment [Line Items]    
Property and equipment, gross 43,417 42,522
Airborne Equipment [Member]    
Property, Plant and Equipment [Line Items]    
Property and equipment, gross 591,297 765,652
Network Equipment [Member]    
Property, Plant and Equipment [Line Items]    
Property and equipment, gross $ 200,140 $ 199,304