Revenue - Contract Balances (Details) - USD ($) $ in Thousands	6 Months Ended
	Mar. 31, 2022	Sep. 30, 2021
Revenue from Contract with Customer [Abstract]
Contract assets	$ 58,553	$ 54,199
Contract liabilities	(56,706)	(42,433)
Net contract asset	1,847	11,766
Revenue recognized related to contract liabilities	33,500
Retention amounts included in accounts receivable	9,800	$ 9,600
Retained amount expected to be collected in the next twelve months	9,100
Retained amount expected to be collected	$ 700