Employee Benefit Plans - Weighted Average Assumptions Used to Determine Benefit Obligation and Net Periodic Benefit Costs (Detail)	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Compensation And Retirement Disclosure [Abstract]
Discount rate	3.50%	4.04%
Rate of compensation increase	3.00%	3.00%

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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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant