Inventories - Additional Information (Detail)	Sep. 30, 2018
Truck, Parts and Other
Inventory [Line Items]
Percentage of inventories valued using LIFO method of accounting	46.00%

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

Name:	us-gaap_InventoryLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration