Commitments and Contingencies - Litigation (Details) £ in Millions	Oct. 12, 2017 GBP (£)
Violations of UK Health and Safety at Work Act 1974 \| Chemviron Carbon Limited (CCL) \| Minimum
Commitments and contingencies
Judgement issued	£ 0.1

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.

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