Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Disaggregation of Revenue [Line Items]
Revenue	$ 27,777	$ 24,873	$ 84,521	$ 81,331
Revenue from Contract with Customer | Transferred over Time
Disaggregation of Revenue [Line Items]
Concentration risk			60.00%
North America
Disaggregation of Revenue [Line Items]
Revenue	24,261	20,301	$ 75,532	68,745
Europe
Disaggregation of Revenue [Line Items]
Revenue	3,516	4,572	8,989	12,586
Fixed wing aircraft
Disaggregation of Revenue [Line Items]
Revenue	13,730	12,557	39,130	38,949
Rotorcraft
Disaggregation of Revenue [Line Items]
Revenue	8,687	5,088	22,348	17,261
Energy components for power generation units
Disaggregation of Revenue [Line Items]
Revenue	3,804	4,887	9,879	13,347
Commercial product and other revenue
Disaggregation of Revenue [Line Items]
Revenue	1,556	2,341	13,164	11,774
Commercial revenue
Disaggregation of Revenue [Line Items]
Revenue	12,266	14,713	34,954	41,213
Military revenue
Disaggregation of Revenue [Line Items]
Revenue	$ 15,511	$ 10,160	$ 49,567	$ 40,118