Inventories - Narrative (Details) - USD ($) $ in Millions	Feb. 28, 2018	Aug. 31, 2017
Inventory Disclosure [Abstract]
LIFO inventory, difference amount had FIFO inventory valuation method been used	$ 243.5	$ 186.2
Percentage of LIFO inventory	16.00%	19.00%

Amount by which inventory stated at last-in first-out (LIFO) is less than (in excess of) inventory stated at other inventory cost methods.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.6(c))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Name:	us-gaap_InventoryLIFOReserve
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant