The percentage of shares reserved for future issuance.

No definition available.

Name:	mist_PercentageOfSharesReservedForFutureIssuance
Namespace Prefix:	mist_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Share Based Compensation Arrangement By Share Based Payment Award Aggregate Number Of Shares Granted To Date

+ References

No definition available.

+ Details

Name:	mist_ShareBasedCompensationArrangementByShareBasedPaymentAwardAggregateNumberOfSharesGrantedToDate
Namespace Prefix:	mist_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the number of options forfeited after termination of one plan became available in 2019 plan.

+ References

No definition available.

+ Details

Name:	mist_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeitedBecameAvailableForIssuance
Namespace Prefix:	mist_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Aggregate number of common shares reserved for future issuance.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.29)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_CommonStockCapitalSharesReservedForFutureIssuance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

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.

+ References

No definition available.

+ Details

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

- Definition

Number of shares authorized for issuance under share-based payment arrangement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of options outstanding, including both vested and non-vested options.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(i)-(ii)
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Percentage of vesting of award under share-based payment arrangement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901

+ Details

Name:	us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_PlanNameAxis=mist_RestatedShareOptionPlan2011Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_EmployeeStockOptionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VestingAxis=us-gaap_ShareBasedCompensationAwardTrancheOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VestingAxis=us-gaap_ShareBasedCompensationAwardTrancheTwoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PlanNameAxis=mist_EquityIncentivePlan2019Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Shareholders' equity - Share-based compensation (Details) - shares	3 Months Ended
	Mar. 31, 2020	Dec. 31, 2019	May 08, 2019	Mar. 31, 2019	Dec. 31, 2018
2011 Plan
Share-based compensation
Options outstanding	2,305,826	2,364,526		2,393,634	2,295,045
2011 Plan \| Options \| Share-based Compensation Award, Tranche One
Share-based compensation
Percentage of shares to vest	25.00%
2011 Plan \| Options \| Share-based Compensation Award, Tranche Two
Share-based compensation
Percentage of shares to vest	2.0833%
2019 Plan
Share-based compensation
Total number of shares available for awards under the plan			2,316,933
Percentage of shares reserved for future issuance			4.00%
Options outstanding	982,550	220,140
Common Stock, Capital Shares Reserved for Future Issuance	980,229
Share-based Compensation Arrangement by Share-based Payment Award, Options Forfeited, Became Available For Issuance	19,077
2019 Plan \| Options
Share-based compensation
Total number of shares available for awards under the plan	3,316,239
Aggregate number of shares granted	2,333,689
2019 Plan \| Options \| Share-based Compensation Award, Tranche One
Share-based compensation
Percentage of shares to vest	25.00%
2019 Plan \| Options \| Share-based Compensation Award, Tranche Two
Share-based compensation
Percentage of shares to vest	2.0833%