Revenue - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2018
Disaggregation Of Revenue [Abstract]
Revenue recognized from performance obligations satisfied in prior periods	$ 1.7	$ 3.0

Amount of revenue recognized arising from contract liability from change in timeframe for performance obligation to be satisfied.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 10
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130551-203045

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