Property, Plant and Equipment - Additional Information (Detail)	3 Months Ended
Mar. 31, 2018 license
United Kingdom
Property, Plant and Equipment [Line Items]
Number of non-operating interest in licenses	2

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration