Commitments and Contingencies - Litigation (Details) - Violations of UK Health and Safety at Work Act 1974 £ in Millions, $ in Millions	Jul. 31, 2017 GBP (£)	Jun. 30, 2017 GBP (£)	Jun. 30, 2017 USD ($)
Accounts payable and accrued liabilities
Commitments and contingencies
Accrued potential loss		£ 0.2	$ 0.3
Chemviron Carbon Limited (CCL) | Minimum
Commitments and contingencies
Possible loss	£ 0.2
Chemviron Carbon Limited (CCL) | Maximum
Commitments and contingencies
Possible loss	£ 2.5