Summary of Significant Accounting Policies - Concentration Risk (Details)	3 Months Ended			6 Months Ended
	Mar. 31, 2022 item customer	Mar. 31, 2021 customer item	Dec. 31, 2020	Mar. 31, 2022 item customer	Mar. 31, 2021 item customer
Concentration of Credit Risk
Number of banks for maintenance of cash balances	2			2
Revenues Net | Customer Concentration Risk
Concentrations
Number of major customers | customer	3	2		2	3
Revenues Net | Customer Concentration Risk | Sierra Nevada Corporation
Concentrations
Concentration of risk (as a percent)					12.00%
Revenues Net | Customer Concentration Risk | Amazon.com, Inc
Concentrations
Concentration of risk (as a percent)	11.00%		14.00%
Revenues Net | Customer Concentration Risk | Pilatus Aircraft Ltd ("Pilatus")
Concentrations
Concentration of risk (as a percent)	29.00%	25.00%		26.00%	17.00%
Revenues Net | Customer Concentration Risk | Textron Aviation, Inc
Concentrations
Concentration of risk (as a percent)	10.00%	16.00%			14.00%
Revenues Net | Customer Concentration Risk | Air Transport Services Group
Concentrations
Concentration of risk (as a percent)				13.00%
Inventory | Supplier Concentration Risk
Concentrations
Number of major suppliers	3	2		3	2