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Discontinued Operations - Narrative (Detail) - USD ($)
 3 Months Ended 12 Months Ended
Aug. 04, 2015
Sep. 30, 2015
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2017
Fiber Optic Licensing Division          
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]          
Sales price of fiber optic licensing operations $ 1,000,000,000        
Net cash proceeds from sale of fiber optic licensing operations $ 848,200,000        
Gain on disposal of discontinued operations before taxes   $ 271,800,000 $ 0 $ 271,833,000  
Tax amount from gain loss of disposal of discontinued operations   100,800,000      
Gain on sale, net of tax   $ 171,000,000      
Assets of fiber optic licensing operations     0   $ 0
Liabilities of discontinued operations     0   $ 0
Telecommunications          
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]          
Legal fees     1,000,000    
Legal fees, net of tax impact     $ 700,000