Components of Net Deferred Tax Assets (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Allowance for doubtful accounts	$ 5.6	$ 5.6
Accrued expenses	1.2	1.1
Settlement accrual	0	59.3
Workers' compensation	8.1	7.0
Amortization of intangible assets	(89.2)	(102.6)
Share-based compensation	3.3	3.9
Net operating loss carryforwards	59.3	5.3
Tax credit carryforwards	2.6	2.1
Other	1.8	1.4
Gross deferred tax assets	171.1	188.3
Valuation Allowance	0.6	0.2
Net deferred tax assets	170.5	188.1
Property and equipment	31.3	24.1
Deferred revenue	(16.8)	(18.5)
Gross deferred tax (liabilities)	48.1	42.6
Net deferred tax assets (liabilities)	$ 122.4	$ 145.5