Property, Plant, and Equipment (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017	Sep. 30, 2017
Property, Plant and Equipment [Abstract]
Depreciation and amortization	$ 13,980	$ 12,958	$ 27,987	$ 25,385
Maintenance and repair expense	5,567	$ 5,354	11,382	$ 10,510
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	477,509		477,509		$ 447,126
Less: accumulated depreciation	(191,822)		(191,822)		(167,083)
Property, plant and equipment, net	285,687		285,687		280,043
Machinery and equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	356,277		356,277		338,056
Land and buildings
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	85,786		85,786		84,282
Construction in process
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 35,446		$ 35,446		$ 24,788