Income Taxes - Summary of Income Tax Examinations (Details)	12 Months Ended
	Sep. 30, 2017
United States | Minimum
Income Tax Examination [Line Items]
Open Tax Year	2017
United States | Maximum
Income Tax Examination [Line Items]
Open Tax Year	2017
China | Minimum
Income Tax Examination [Line Items]
Open Tax Year	2007
China | Maximum
Income Tax Examination [Line Items]
Open Tax Year	2017
South Korea | Minimum
Income Tax Examination [Line Items]
Open Tax Year	2010
South Korea | Maximum
Income Tax Examination [Line Items]
Open Tax Year	2017
Taiwan | Minimum
Income Tax Examination [Line Items]
Open Tax Year	2012
Taiwan | Maximum
Income Tax Examination [Line Items]
Open Tax Year	2017