Property, Plant and Equipment (Details) $ in Thousands	Sep. 30, 2017 USD ($) item	Sep. 30, 2016 USD ($)
Property, plant and equipment
Gross amount	$ 348,777	$ 335,829
Less accumulated depreciation	(156,221)	(136,647)
Net amount	192,556	199,182
Shanghai
Property, plant and equipment
Assets under a capital lease	275
La Porte
Property, plant and equipment
Assets under a capital lease	$ 7,913
Number of leased buildings | item	2
Land and land improvements
Property, plant and equipment
Gross amount	$ 9,345	7,207
Buildings and improvements
Property, plant and equipment
Gross amount	44,705	37,343
Machinery and equipment
Property, plant and equipment
Gross amount	289,035	262,717
Construction in process
Property, plant and equipment
Gross amount	$ 5,692	$ 28,562