Commitments - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Sep. 30, 2012 Employee	Sep. 30, 2011	Sep. 30, 2010
Commitments and Contingencies Disclosure [Line Items]
Contractual sublease commitments in 2013	$ 1.5
Contractual sublease commitments in 2014	1.0
Rent expense under operating leases	$ 21.3	$ 21.1	$ 22.6
Number of executives in a management agreement providing for certain payments and other benefits in the event of a qualified change	26