Retirement Plans - Schedule of Actuarial Assumptions Used in Determination of Projected Benefit Obligation (Detail)	Dec. 31, 2017	Dec. 31, 2016
Retirement Benefits [Abstract]
Weighted average discount rate	3.53%	3.96%
Rates of average increase in compensation levels	3.50%	3.50%

Weighted average rate increase of compensation, used to determine benefit obligation of defined benefit plan. Plan includes, but is not limited to, pay-related defined benefit plan.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (k)(2)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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Data Type:	num:percentItemType
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Period Type:	instant