Debt and Credit Facilities (Applicable Margin for Borrowings) (Detail) (USD $)	9 Months Ended
	Jun. 30, 2014		Sep. 30, 2013
Term Loan Facility Due August Seventh Twenty Ninteen [Member]
Line of Credit Facility [Line Items]
Applicable margin rate	2.75%
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 75,000,000
Letters of credit, outstanding	5,700,000
Credit Facility, net of unamortized original issue discount of $1.0 million and $1.2 million respectively.	477,567,000		481,016,000
Credit facility, commitment fee percentage for unused capacity	0.375%
Revolving Credit Facility [Member] | Minimum
Line of Credit Facility [Line Items]
Credit facility, commitment fee percentage for unused capacity	0.25%
Revolving Credit Facility [Member] | Maximum
Line of Credit Facility [Line Items]
Credit facility, commitment fee percentage for unused capacity	0.375%
Base Rate Margin | Term Loan Facility Due August Seventh Twenty Ninteen [Member]
Line of Credit Facility [Line Items]
Applicable margin rate	1.75%
Base Rate Margin | Revolving facility due March 2015 | Minimum
Line of Credit Facility [Line Items]
Applicable margin rate	0.50%	[1]
Base Rate Margin | Revolving facility due March 2015 | Maximum
Line of Credit Facility [Line Items]
Applicable margin rate	0.75%	[1]
LIBOR Margin | Term Loan Facility Due August Seventh Twenty Ninteen [Member]
Line of Credit Facility [Line Items]
Applicable margin rate	2.75%
LIBOR Margin | Term loans maturing March 2013
Line of Credit Facility [Line Items]
Debt Instrument, Interest Rate, Effective Percentage	2.90%
LIBOR Margin | Revolving facility due March 2015 | Minimum
Line of Credit Facility [Line Items]
Applicable margin rate	1.50%	[1]
LIBOR Margin | Revolving facility due March 2015 | Maximum
Line of Credit Facility [Line Items]
Applicable margin rate	1.75%	[1]
Debt Instrument Amended And Restated [Member] | Term loans maturing March 2016
Line of Credit Facility [Line Items]
Credit Facility, net of unamortized original issue discount of $1.0 million and $1.2 million respectively.	$ 478,600,000

[1] The margin is determined based on our net leverage ratio at the date the interest rates are reset on the revolving credit line.