Summary of Significant Accounting Policies - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Revenue from External Customer [Line Items]
Retention amounts included in accounts receivable	$ 6,900	$ 5,600
Retained amount expected to be collected in the next twelve months	5,900
Retained amount expected to be collected	$ 1,000
Warranty for parts and services date of shipment	18 months
Warranty parts and services date of energization	12 months
Research and development expenses	$ 6,265	6,327	$ 6,717
Minimum
Revenue from External Customer [Line Items]
Long-term contract beginning	1 month
Accounts Receivable
Revenue from External Customer [Line Items]
Retention amounts included in accounts receivable	$ 6,900	$ 5,600
Other Assets
Revenue from External Customer [Line Items]
Retained amount expected to be collected	$ 1,000