Components of Accrued Expenses and Other Current Liabilities (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Sep. 30, 2016
Accrued Expenses and Other Current Liabilities [Line Items]
Accrued wages and benefits	$ 24,425	$ 22,237
Accrued insurance and environmental costs	68,760	70,037
Other accrued expenses and other current liabilities	15,264	11,581
Total accrued expenses and other current liabilities	$ 108,449	$ 103,855