Fair Value Measures (Assets and Liabilities Measured at Fair Value on Recurring Basis) (Detail) - USD ($)		6 Months Ended
		Mar. 31, 2016	Sep. 30, 2015
Fair Value, Measurements, Recurring
Assets:
Money market funds	[1]	$ 150,842,000	$ 334,404,000
US government agency securities	[1]	1,001,000	1,000,000
Bank Time Deposits, Fair Value Disclosure		51,288,000	71,453,000
Commercial Paper, Fair value		1,769,000	3,493,000
Corporate notes and bonds, Fair Value		47,577,000	44,533,000
Foreign Currency Contract, Asset, Fair Value Disclosure	[2]	1,798,000	260,000
Total assets at fair value		254,275,000	455,143,000
Liabilities:
Contingent earn-out		(20,825,000)	(15,961,000)
Total liabilities at fair value		(20,825,000)	(15,961,000)
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1
Assets:
Money market funds		150,842,000	334,404,000
US government agency securities		1,001,000	1,000,000
Bank Time Deposits, Fair Value Disclosure		0	0
Commercial Paper, Fair value		0	0
Corporate notes and bonds, Fair Value		0	0
Foreign Currency Contract, Asset, Fair Value Disclosure		0	0
Total assets at fair value		151,843,000	335,404,000
Liabilities:
Contingent earn-out		0	0
Total liabilities at fair value		0	0
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2
Assets:
Money market funds		0	0
US government agency securities		0	0
Bank Time Deposits, Fair Value Disclosure		51,288,000	71,453,000
Commercial Paper, Fair value		1,769,000	3,493,000
Corporate notes and bonds, Fair Value		47,577,000	44,533,000
Foreign Currency Contract, Asset, Fair Value Disclosure		1,798,000	260,000
Total assets at fair value		102,432,000	119,739,000
Liabilities:
Contingent earn-out		0	0
Total liabilities at fair value		0	0
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3
Assets:
Money market funds		0	0
US government agency securities		0	0
Bank Time Deposits, Fair Value Disclosure		0	0
Commercial Paper, Fair value		0	0
Corporate notes and bonds, Fair Value		0	0
Foreign Currency Contract, Asset, Fair Value Disclosure		0	0
Total assets at fair value		0	0
Liabilities:
Contingent earn-out		(20,825,000)	(15,961,000)
Total liabilities at fair value		(20,825,000)	(15,961,000)
Corporate Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Amortized Cost Basis		47,588,000	44,581,000
Commercial Paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Amortized Cost Basis		$ 1,769,000	$ 3,491,000
Commercial paper, corporate notes and bonds [Member]
Liabilities:
Available for sale Securities, Weighted Average Maturity		1 year 3 months 1 day

[1] Money market funds and U.S. government agency securities, included in cash and cash equivalents in the accompanying balance sheets, are valued at quoted market prices in active markets.

[2] The fair values of our time deposits, commercial paper, corporate notes and bonds, and foreign currency exchange contracts are based on the most recent observable inputs for similar instruments in active markets or quoted prices for identical or similar instruments in markets that are not active or are directly or indirectly observable. Time deposits are generally for terms of one year or less. The commercial paper and corporate notes and bonds mature within three years and have a weighted average maturity of 1.25 years as of March 31, 2016.