Summary of Significant Accounting Policies - Concentration Risk (Details)	3 Months Ended
	Dec. 31, 2020 customer item	Dec. 31, 2019 customer item
Concentration of Credit Risk
Number of banks for maintenance of cash balances	2
Net sales | Major Customers and Products
Concentrations
Number of major customers | customer	3	2
Net sales | Major Customers and Products | Sierra Nevada Corporation
Concentrations
Concentration of risk (as a percent)	17.00%
Net sales | Major Customers and Products | Amazon.con, Inc
Concentrations
Concentration of risk (as a percent)	12.00%
Net sales | Major Customers and Products | Textron Aviation, Inc
Concentrations
Concentration of risk (as a percent)	11.00%
Net sales | Major Customers and Products | Pilatus Aircraft Ltd ("Pilatus")
Concentrations
Concentration of risk (as a percent)		32.00%
Net sales | Major Customers and Products | Empresa Nacional de Aeronautica
Concentrations
Concentration of risk (as a percent)		22.00%
Inventory | Major Suppliers
Concentrations
Concentration of risk (as a percent)	10.00%	10.00%
Number of major suppliers	2	1