Segment Reporting, Geographic Information and Concentration of Credit Risk - Additional Information (Detail) - Customer	3 Months Ended	12 Months Ended
Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Segment Reporting [Abstract]
Concentration Risk, Customer	No customer accounted for 10% or more of net revenue for either of the three months ended March 31, 2019 or 2018. One customer accounted for 10% of net accounts receivable at March 31, 2019. No customer accounted for 10% or more of net accounts receivable balance at December 31, 2018.
Number of major customer represented stated percentage of total net revenue	0	0
Number of customers who accounted for 10% or more net accounts receivable	1		0

Description of risks that arise due to the volume of business transacted with a particular customer. At a minimum, the description informs financial statement users of the general nature of the risk, but excludes "Information about Major Customers" that may be disclosed elsewhere (for instance, segment disclosures).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 18
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=99393423&loc=d3e6351-108592

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=99393423&loc=d3e6404-108592

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 16
-URI http://asc.fasb.org/extlink&oid=99393423&loc=d3e6327-108592

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