Revenue - Contract Balances (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Jun. 30, 2020	Jun. 30, 2020	Sep. 30, 2019
Revenue from Contract with Customer [Abstract]
Contract assets	$ 51,723	$ 51,723	$ 55,374
Contract liabilities	(97,969)	(97,969)	(71,464)
Net contract liability	(46,246)	(46,246)	(16,090)
Revenue recognized related to contract liabilities	34,600	67,100
Retention amounts included in accounts receivable	6,700	6,700	$ 5,600
Retained amount expected to be collected in the next twelve months	5,600	5,600
Retained amount expected to be collected	$ 1,100	$ 1,100