Summary of Significant Accounting Policies - Concentration Risk (Details)	3 Months Ended		12 Months Ended
	Dec. 31, 2018 customer item	Dec. 31, 2017 customer item	Sep. 30, 2018
Concentration of Credit Risk
Number of banks for maintenance of cash balances | item	2
Major Suppliers
Concentrations
Number of major suppliers | item	1	1
Net sales | Major Customers and Products
Concentrations
Number of major customers | customer	3	1
Net sales | Major Customers and Products | Air Transport Services Group
Concentrations
Concentration of risk (as a percent)	30.00%
Net sales | Major Customers and Products | Pilatus Aircraft Ltd ("Pilatus")
Concentrations
Concentration of risk (as a percent)	21.00%
Net sales | Major Customers and Products | DHL
Concentrations
Concentration of risk (as a percent)	12.00%
Net sales | Major Customers and Products | S&K Aerospace LLC
Concentrations
Concentration of risk (as a percent)		10.00%
Accounts receivable | Major Customers and Products
Concentrations
Number of major customers | customer	1
Concentration of risk (as a percent)	29.00%		27.00%
Inventory | Major Suppliers
Concentrations
Concentration of risk (as a percent)	10.00%	14.00%