Goodwill and Other Intangible Assets - Narrative (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Schedule Of Other Intangible Assets [Line Items]
Goodwill impairment non-cash charges			$ 21.3
Amortization expense for other intangible assets	$ 7.1	$ 8.0	21.6	$ 25.7
Strategic Services
Schedule Of Other Intangible Assets [Line Items]
Goodwill impairment non-cash charges	$ 21.3		$ 21.3