Government assistance (Details) - USD ($) $ in Thousands	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018
Government assistance
Research and development expenditures eligible for investment tax credits	$ 270	$ 195

Provincial refundable tax credit based on incurred research and development expenditures, recorded as a reduction to research and development expenses.

No definition available.

Name:	mist_ResearchAndDevelopmentExpensesExpendituresEligibleForTaxCredits
Namespace Prefix:	mist_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration