Financial Assets Measured at Fair Value on a Recurring Basis (Detail) (Fair Value, Measurements, Recurring, USD $) In Thousands, unless otherwise specified	Mar. 31, 2012		Sep. 30, 2011
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total	$ 138,672		$ 177,500
Cash equivalents
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	88,587	[1]	67,504	[1]
U.S. certificates of deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities available-for-sale	5,001	[2]
U.S. corporate debt
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities available-for-sale	2,023	[2]	1,529	[2]
U.S. commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities available-for-sale	10,998	[2]	13,993	[2]
Non-U.S. commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities available-for-sale	4,997	[2]
U.S. government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities available-for-sale	22,030	[2]	44,092	[2]
U.S. municipal obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities available-for-sale			46,212	[2]
Marketable securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities available-for-sale	5,036	[3]	4,170	[3]
Active Markets for Identical Instruments (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total	93,623		71,674
Active Markets for Identical Instruments (Level 1) | Cash equivalents
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	88,587	[1]	67,504	[1]
Active Markets for Identical Instruments (Level 1) | Marketable securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities available-for-sale	5,036	[3]	4,170	[3]
Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total	45,049		105,826
Significant Other Observable Inputs (Level 2) | U.S. certificates of deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities available-for-sale	5,001	[2]
Significant Other Observable Inputs (Level 2) | U.S. corporate debt
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities available-for-sale	2,023	[2]	1,529	[2]
Significant Other Observable Inputs (Level 2) | U.S. commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities available-for-sale	10,998	[2]	13,993	[2]
Significant Other Observable Inputs (Level 2) | Non-U.S. commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities available-for-sale	4,997	[2]
Significant Other Observable Inputs (Level 2) | U.S. government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities available-for-sale	22,030	[2]	44,092	[2]
Significant Other Observable Inputs (Level 2) | U.S. municipal obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities available-for-sale			$ 46,212	[2]

[1] Included in cash and cash equivalents on our balance sheet at March 31, 2012 and September 30, 2011. Not included in this table are cash deposits of $57.4 million and $68.2 million at March 31, 2012 and September 30, 2011, respectively.

[2] Included in current marketable securities on our balance sheet at March 31, 2012 and September 30, 2011.

[3] Represents securities held under a supplemental retirement and savings plan for certain officers and senior management employees, which are distributed upon termination or retirement of the employees. Included in long-term marketable securities on our balance sheet at March 31, 2012 and September 30, 2011.