Revenue Recognition - Schedule of Significant Changes in Contract Assets and Deferred Revenue (Detail) $ in Thousands	9 Months Ended
Sep. 30, 2018 USD ($)
Changes in the Contract Assets
Transferred to receivables from contract assets recognized at December 31, 2017	$ 263
Changes in the Contract Liabilities
Revenue recognized that was included in deferred revenue at December 31, 2017	$ 2,847

Amount of decrease in right to consideration in exchange for good or service transferred to customer when right is conditioned on something other than passage of time from transfer to receivable due to right to consideration becoming unconditional.

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 (d)
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130551-203045

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