Summary of Significant Accounting Policies - Concentration Risk (Details)	3 Months Ended		9 Months Ended
	Jun. 30, 2020 customer item	Jun. 30, 2019 customer item	Jun. 30, 2020 customer item	Jun. 30, 2019 customer item
Concentration of Credit Risk
Number of banks for maintenance of cash balances	2		2
Net sales | Major Customers and Products
Concentrations
Number of major customers | customer	2	1	2	2
Net sales | Major Customers and Products | Pilatus Aircraft Ltd ("Pilatus")
Concentrations
Concentration of risk (as a percent)	36.60%	32.00%		29.00%
Net sales | Major Customers and Products | Empresa Nacional de Aeronautica
Concentrations
Concentration of risk (as a percent)	10.90%
Net sales | Major Customers and Products | Air Transport Services Group
Concentrations
Concentration of risk (as a percent)			35.50%	15.00%
Net sales | Major Customers and Products | Deutsche Post DHL Group
Concentrations
Concentration of risk (as a percent)			12.90%
Inventory | Major Suppliers
Concentrations
Concentration of risk (as a percent)	10.00%	10.00%	10.00%	10.00%
Number of major suppliers	4	2	3	2