Commitments and Contingencies - Additional Information (Detail) $ in Millions	12 Months Ended
Dec. 31, 2018 USD ($)
Commitments And Contingencies Disclosure [Abstract]
Cash compensation on termination of employment, maximum	$ 25

Amount of increase in benefit obligation for benefits provided to employees payable from defined benefit plan or payable upon retirement.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a)(10)
-URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920

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