Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Disaggregation of Revenue [Line Items]
Revenue	$ 27,392	$ 27,794	$ 56,458	$ 52,044
Commercial revenue
Disaggregation of Revenue [Line Items]
Revenue	14,435	15,393	26,500	29,033
Military revenue
Disaggregation of Revenue [Line Items]
Revenue	12,957	12,401	29,958	23,011
Fixed wing aircraft
Disaggregation of Revenue [Line Items]
Revenue	13,088	15,092	26,392	27,623
Rotorcraft
Disaggregation of Revenue [Line Items]
Revenue	7,043	5,332	12,173	10,813
Energy components for power generation units
Disaggregation of Revenue [Line Items]
Revenue	4,730	6,132	8,460	11,640
Commercial product and other revenue
Disaggregation of Revenue [Line Items]
Revenue	2,531	1,238	9,433	1,968
North America
Disaggregation of Revenue [Line Items]
Revenue	22,721	22,081	48,443	41,323
Europe
Disaggregation of Revenue [Line Items]
Revenue	$ 4,671	$ 5,713	$ 8,015	$ 10,721
Transferred over Time | Revenue from Contract with Customer
Disaggregation of Revenue [Line Items]
Concentration risk			60.00%