Fair Value Measurements - Assets and Liabilities Measured at Fair Value (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013
Assets
Available-for-sale securities	$ 151,342	$ 90,391
Fair Value, Measurements, Recurring
Assets
Cash equivalents	6,404	7,754
Available-for-sale securities	151,342	90,391
Foreign exchange contracts		31
Total Assets	157,746	98,176
Liabilities
Foreign exchange contracts	58	5
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets
Cash equivalents	5,166	6,152
Available-for-sale securities	0	2,199
Foreign exchange contracts		0
Total Assets	5,166	8,351
Liabilities
Foreign exchange contracts		0
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2)
Assets
Cash equivalents	1,238	1,602
Available-for-sale securities	151,342	88,192
Foreign exchange contracts		31
Total Assets	152,580	89,825
Liabilities
Foreign exchange contracts	58	5
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3)
Assets
Cash equivalents		0
Available-for-sale securities	0	0
Foreign exchange contracts		0
Total Assets	0	0
Liabilities
Foreign exchange contracts	0	0
Fair Value, Measurements, Nonrecurring | Significant Unobservable Inputs (Level 3)
Assets
Note receivable	$ 1,007