Business and Basis of Consolidation- Additional Information (Detail)	12 Months Ended
Dec. 31, 2017 Segment
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Number Of Reporting Units	4

Number of reporting units tested for impairment of goodwill. A reporting unit is an operating segment or one level below an operating segment.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Reporting Unit
-URI http://asc.fasb.org/extlink&oid=6523643

Name:	us-gaap_NumberOfReportingUnits
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration