Government assistance (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Government assistance
Research and development expenditures eligible for investment tax credits	$ 106	$ 78

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