Components of Net Deferred Tax Assets (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Sep. 30, 2011
Schedule of Deferred Tax Assets and Liabilities [Line Items]
Allowance for doubtful accounts	$ 8.2	$ 6.8
Accrued expenses, Current	1.2	2.0
Workers' compensation, Current	6.7	6.1
Deferred revenue, Current	(22.0)	(24.5)
Other, Current	0.3	(2.1)
Current portion of deferred tax assets (liabilities)	(5.6)	(11.7)
Amortization of intangible assets, Non current	114.0	92.9
Property and equipment, Non current	(32.4)	(37.0)
Share-based compensation, Non current	5.2	7.6
Other, Non current	2.2	1.1
Capital loss carry forward		0.1
NOL carry forward, expiring beginning in 2012, Non current	4.0	4.7
Less: valuation allowance	(0.2)	(0.8)	(1.9)
Noncurrent portion of deferred tax assets (liabilities):	92.8	68.6
Net deferred tax assets (liabilities)	$ 87.2	$ 56.9