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