Summary of Significant Accounting Policies - Concentration Risk (Details)	3 Months Ended		9 Months Ended
	Jun. 30, 2019 customer item	Jun. 30, 2018 customer item	Jun. 30, 2019 customer item	Jun. 30, 2018 customer item
Concentration of Credit Risk
Number of banks for maintenance of cash balances	2		2
Major Suppliers
Concentrations
Number of major suppliers	3	3	2	2
Net sales | Major Customers and Products
Concentrations
Number of major customers | customer	1	3	2	1
Net sales | Major Customers and Products | Pilatus Aircraft Ltd ("Pilatus")
Concentrations
Concentration of risk (as a percent)	32.00%	26.00%	29.00%	17.00%
Net sales | Major Customers and Products | Air Transport Services Group
Concentrations
Concentration of risk (as a percent)			15.00%
Net sales | Major Customers and Products | L3
Concentrations
Concentration of risk (as a percent)		15.00%
Net sales | Major Customers and Products | DoD
Concentrations
Concentration of risk (as a percent)		12.00%
Inventory | Major Suppliers
Concentrations
Concentration of risk (as a percent)	10.00%	10.00%	10.00%	10.00%