Components of Net Deferred Tax Assets (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Allowance for doubtful accounts	$ 6.9	$ 6.4
Accrued payroll & employee benefits	11.4	5.1
Workers' compensation	10.9	9.8
Amortization of intangible assets	56.3	72.2
Share-based compensation	7.8	5.0
Net operating loss carryforwards	44.2	48.5
Tax credit carryforwards	4.8	4.7
Other	1.1	4.0
Gross deferred tax assets	143.4	155.7
Valuation Allowance	0.4	0.3
Net deferred tax assets	143.0	155.4
Property and equipment	7.8	9.5
Deferred revenue	(23.2)	(18.5)
Investment in partnerships	3.2	0.2
Other liabilities	0.9	2.0
Gross deferred tax (liabilities)	35.1	30.2
Net deferred tax assets (liabilities)	$ 107.9	$ 125.2