Inventories - Additional Information (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Inventory Disclosure [Abstract]
Inventory recorded on FIFO method	$ 170.5	$ 95.6
Inventory recorded on average cost method	$ 151.6	$ 127.9

The amount of weighted average cost inventory present at the reporting date when inventory is valued using different valuation methods.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6361739&loc=d3e7789-107766

Name:	us-gaap_WeightedAverageCostInventoryAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant