Short and Long-Term Debt - Short-Term Debt Additional Information (Detail) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
Feb. 28, 2015	Dec. 31, 2017
Debt Disclosure [Abstract]
Average month-end balance		$ 0.1
Maximum month-end balance	$ 0.2

For the form of debt having an initial term of less than one year or less than the normal operating cycle, if longer, maximum month-end borrowings during the period.

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(19))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Name:	us-gaap_ShorttermDebtMaximumMonthendOutstandingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration