Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues.

No definition available.

Name:	us-gaap_NumberOfOperatingSegments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

Segment Information - Additional Information (Detail)	3 Months Ended		9 Months Ended
Segment Information - Additional Information (Detail)	Sep. 30, 2018 Country Customer	Sep. 30, 2017 Country Customer	Sep. 30, 2018 Segment Country Customer	Sep. 30, 2017 Country Customer	Dec. 31, 2017 Country
Segment Reporting Information
Number of operating segments \| Segment			1
Geographic Concentration Risk
Segment Reporting Information
Number Of Individual Country accounted for 10% or more of total revenues	0	0	0	0
Number Of Individual country accounted for 10% or more of total consolidated assets	0		0		0
Customer Concentration Risk \| Sales Revenue, Goods, Net
Segment Reporting Information
Number Of Individual Customer accounted for 10% or more of total consolidated revenues \| Customer	0	0	0	0