Revenue Recognition - Summary of Changes in Certain Contract Assets and Liabilities (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Accounts receivable	$ 45,052	$ 34,487
Deferred revenue	(2,735)	(5,015)
Deferred expenses	315	377
Customer prepayments	(1,707)	$ (776)
Sales allowances	(567)
Accounting Standards Update 2014-09 [Member]
Disaggregation of Revenue [Line Items]
Accounts receivable	10,565
Deferred revenue	2,280
Deferred expenses	(62)
Customer prepayments	(931)
Sales allowances	$ (567)

Amount due from customers or clients, within one year of the balance sheet date (or the normal operating cycle, whichever is longer), for goods or services (including trade receivables) that have been delivered or sold in the normal course of business, reduced to the estimated net realizable fair value by an allowance established by the entity of the amount it deems uncertain of collection.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-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

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(3))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Name:	us-gaap_AccountsReceivableNetCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant