Revenue - Schedule of Accounts Receivable and Deferred Revenues (Detail) $ in Thousands	6 Months Ended
Jun. 30, 2018 USD ($)
Deferred Revenue - Short Term
Contract With Customer Asset And Liability [Line Items]
Deferred Revenue, Beginning balance	$ 74,332
Net increase (decrease) during the period	9,546
Deferred Revenue, Ending balance	83,878
Deferred Revenue - Long Term
Contract With Customer Asset And Liability [Line Items]
Deferred Revenue, Beginning balance	2,049
Net increase (decrease) during the period	(548)
Deferred Revenue, Ending balance	$ 1,501

Amount of obligation to transfer good or service to customer for which consideration has been received or is receivable.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=82913815&loc=SL49130531-203044

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=82913815&loc=SL49130532-203044

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 8
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130549-203045

Name:	us-gaap_ContractWithCustomerLiability
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant