Postretirement Benefits - Fair Value of Pension Assets by Asset Category and by Level (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 4,734	$ 4,838	$ 6,131
Other Investments | Swiss Life collective foundation
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	4,208	4,347
Other Investments | Taiwan collective trust
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	526	491
Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 1 | Other Investments | Swiss Life collective foundation
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 1 | Other Investments | Taiwan collective trust
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	4,734	4,838
Level 2 | Other Investments | Swiss Life collective foundation
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	4,208	4,347
Level 2 | Other Investments | Taiwan collective trust
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	526	491
Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Fair Value, Inputs, Level 3 [Member] | Other Investments | Swiss Life collective foundation
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Fair Value, Inputs, Level 3 [Member] | Other Investments | Taiwan collective trust
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 0	$ 0