Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Disaggregation of Revenue [Line Items]
Revenue	$ 24,866	$ 30,537	$ 49,944	$ 56,744
Revenue from Contract with Customer | Transferred over Time
Disaggregation of Revenue [Line Items]
Concentration risk			61.00%	63.00%
North America
Disaggregation of Revenue [Line Items]
Revenue	20,019	27,495	$ 39,784	$ 51,271
Europe
Disaggregation of Revenue [Line Items]
Revenue	4,847	3,042	10,160	5,473
Fixed wing aircraft
Disaggregation of Revenue [Line Items]
Revenue	10,176	14,065	19,966	25,400
Rotorcraft
Disaggregation of Revenue [Line Items]
Revenue	7,872	6,813	15,603	13,661
Energy components for power generation units
Disaggregation of Revenue [Line Items]
Revenue	5,102	3,417	11,565	6,074
Commercial product and other revenue
Disaggregation of Revenue [Line Items]
Revenue	1,716	6,242	2,810	11,609
Commercial revenue
Disaggregation of Revenue [Line Items]
Revenue	9,247	12,497	20,000	22,688
Military revenue
Disaggregation of Revenue [Line Items]
Revenue	$ 15,619	$ 18,040	$ 29,944	$ 34,056