Postretirement Benefits - Fair Value of Pension Assets by Asset Category and by Level (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 6,131	$ 5,996	$ 8,015
Other Investments | Swiss Life collective foundation
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	5,608
Other Investments | Taiwan collective trust
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	523
Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	6,131
Level 2 | Other Investments | Swiss Life collective foundation
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	5,608
Level 2 | Other Investments | Taiwan collective trust
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 523