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Goodwill and Other Intangible Assets - Narrative (Detail) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Schedule Of Other Intangible Assets [Line Items]      
Amortization expense for other intangible assets $ 19.3 $ 21.6 $ 25.4
Disposition by Sale | GDS Business      
Schedule Of Other Intangible Assets [Line Items]      
Reduced in goodwill   408.9  
Reduced in accumulated Impairment loss   408.9  
Reduced in accumulated amortization   70.9  
Disposition by Sale | GDS Business | Client Relationships      
Schedule Of Other Intangible Assets [Line Items]      
Reduced in intangible asset   $ 70.9