Restructuring, Impairment and Other Charges - Narrative (Detail)	3 Months Ended		9 Months Ended
	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($) Facility	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($) Facility	Dec. 31, 2016 USD ($)
Restructuring Cost And Reserve [Line Items]
Employee termination costs	$ 10,700,000	$ 9,700,000	$ 19,500,000	$ 20,700,000
Impairment charges	21,500,000	(100,000)	21,700,000	(1,000,000)
Goodwill impairment charges			21,300,000
Goodwill	587,600,000		587,600,000		$ 602,000,000
Other restructuring charges	1,100,000	$ 600,000	3,800,000	$ 2,900,000
Number of facilities closed | Facility		2		2
Strategic Services
Restructuring Cost And Reserve [Line Items]
Goodwill impairment charges	21,300,000		21,300,000
Goodwill	195,200,000		195,200,000		$ 216,500,000
Strategic Services | Digital And Creative Solutions
Restructuring Cost And Reserve [Line Items]
Impairment charges	(21,500,000)		(21,700,000)
Goodwill impairment charges	21,300,000		21,300,000
Goodwill	$ 0		$ 0