Commitment and Contingencies - Additional Information (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Sep. 30, 2018
Commitments And Contingencies [Line Items]
Reserve for unpaid and incurred but not reported claims, amount	$ 126,178	$ 127,937
Reserve for unpaid and incurred but not reported claims, classified in current liabilities	40,283	34,537
Reserve for unpaid and incurred but not reported claims, classified in non-current liabilities	85,895	93,400
Claims recoverable from third party insurance carriers	34,192
Other Current Assets
Commitments And Contingencies [Line Items]
Claims recoverable from third party insurance carriers	6,926	17,462
Other Assets
Commitments And Contingencies [Line Items]
Claims recoverable from third party insurance carriers	$ 27,266	$ 19,558