Concentration of Credit Risk - External net revenue, net of intercompany eliminations, and net asset information by region (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	$ 1,464,429	$ 1,429,456	$ 1,444,441
Net Assets	582,219	482,063
Property, plant, and equipment, net	374,988	364,461
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	1,174,474	1,164,634	1,147,649
Net Assets	462,883	408,330
Property, plant, and equipment, net	357,597	347,832
Rest of World
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	289,955	264,822	$ 296,792
Net Assets	119,336	73,733
Property, plant, and equipment, net	$ 17,391	$ 16,629