Long-Term Debt - Additional information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Sep. 30, 2012	Apr. 16, 2012	Dec. 21, 2011
Debt Instrument [Line Items]
Aggregate amount of revolving loan commitments		$ 600	$ 500
Credit facility, maturity date	December 2016
Increase in loan commitments	250
Sub-limit for swing line advances			10
Sub-limit for letters of credit			100
Increase in loan commitments under credit facility		100
Loan commitments may be increased		150
Outstanding balance on the credit facility	416.5
Outstanding standby letters of credit under the credit facility	2.0
Credit facility, remaining borrowing capacity	$ 181.5
Federal funds rate plus	0.005
Adjusted LIBOR rate plus	1.00%
LIBOR Rate plus, Varying margin, minimum	1.75%
LIBOR Rate plus, Varying margin, maximum	2.75%
Consolidated leverage ratio, minimum	5.00
Consolidated leverage ratio, maximum	1.00
Interest coverage ratio, minimum	2.50
Interest coverage ratio, maximum	1.00
Minimum
Debt Instrument [Line Items]
Commitment fee, percentage	0.30%
Maximum
Debt Instrument [Line Items]
Commitment fee, percentage	0.50%
Credit Facility
Debt Instrument [Line Items]
Adjusted LIBOR rate plus, varying margin, minimum	0.75%
Adjusted LIBOR rate plus, varying margin, maximum	1.75%
Swing Line Loans
Debt Instrument [Line Items]
Adjusted LIBOR rate plus, varying margin, minimum	0.75%
Adjusted LIBOR rate plus, varying margin, maximum	1.75%