Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Disaggregation of Revenue [Line Items]
Revenue	$ 30,537	$ 27,392	$ 56,744	$ 56,458
Revenue from Contract with Customer | Transferred over Time
Disaggregation of Revenue [Line Items]
Concentration risk			63.00%
North America
Disaggregation of Revenue [Line Items]
Revenue	27,495	22,721	$ 51,271	48,443
Europe
Disaggregation of Revenue [Line Items]
Revenue	3,042	4,671	5,473	8,015
Fixed wing aircraft
Disaggregation of Revenue [Line Items]
Revenue	14,065	13,088	25,400	26,392
Rotorcraft
Disaggregation of Revenue [Line Items]
Revenue	6,813	7,043	13,661	12,173
Energy components for power generation units
Disaggregation of Revenue [Line Items]
Revenue	3,417	4,730	6,074	8,460
Commercial product and other revenue
Disaggregation of Revenue [Line Items]
Revenue	6,242	2,531	11,609	9,433
Commercial revenue
Disaggregation of Revenue [Line Items]
Revenue	12,497	14,435	22,688	26,500
Military revenue
Disaggregation of Revenue [Line Items]
Revenue	$ 18,040	$ 12,957	$ 34,056	$ 29,958