Revenue - Contract Balances (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2019	Sep. 30, 2019
Revenue from Contract with Customer [Abstract]
Contract assets	$ 60,296	$ 55,374
Contract liabilities	(77,556)	(71,464)
Net contract asset (liability)	(17,260)	(16,090)
Revenue recognized related to contract liabilities	45,600
Retention amounts included in accounts receivable	5,900	$ 5,600
Retained amount expected to be collected in the next twelve months	5,600
Retained amount expected to be collected in 2021	$ 300