Fair Value Measures (Assets and Liabilities Measured at Fair Value on Recurring Basis) (Detail) - USD ($)	3 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale Securities, Weighted Average Maturity	6 months 5 days	7 months 10 days
Document Period End Date	Dec. 31, 2018
Fair Value, Measurements, Recurring
Assets:
Money market funds	$ 185,713,000	$ 200,004,000
Bank Time Deposits, Fair Value Disclosure	97,743,000	88,158,000
Commercial Paper, Fair value	20,287,000	27,363,000
Corporate notes and bonds, Fair Value	58,153,000	57,417,000
Foreign Currency Contract, Asset, Fair Value Disclosure	463,000	143,000
Total assets at fair value	362,359,000	373,085,000
Liabilities:
Contingent earn-out	(3,979,000)	(4,000,000)
Foreign Currency Contracts, Liability, Fair Value Disclosure	(130,000)	(1,192,000)
Total liabilities at fair value	(4,109,000)	(5,192,000)
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1
Assets:
Money market funds	185,713,000	200,004,000
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	185,713,000	200,004,000
Liabilities:
Contingent earn-out	0	0
Foreign Currency Contracts, Liability, Fair Value Disclosure	0	0
Total liabilities at fair value	0	0
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2
Assets:
Money market funds	0	0
Bank Time Deposits, Fair Value Disclosure	97,743,000	88,158,000
Commercial Paper, Fair value	20,287,000	27,363,000
Corporate notes and bonds, Fair Value	58,153,000	57,417,000
Foreign Currency Contract, Asset, Fair Value Disclosure	463,000	143,000
Total assets at fair value	176,646,000	173,081,000
Liabilities:
Contingent earn-out	0	0
Foreign Currency Contracts, Liability, Fair Value Disclosure	(130,000)	(1,192,000)
Total liabilities at fair value	(130,000)	(1,192,000)
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3
Assets:
Money market funds	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	(3,979,000)	(4,000,000)
Foreign Currency Contracts, Liability, Fair Value Disclosure	0	0
Total liabilities at fair value	(3,979,000)	(4,000,000)
Corporate Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Amortized Cost Basis		57,563,000
Commercial Paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Amortized Cost Basis		$ 27,194,000
Commercial paper, corporate notes and bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale Securities, Weighted Average Maturity