The term of agreement to issue shares of common stock.

No definition available.

Name:	mrns_CommonStockAuthorizedTermOfAgreement
Namespace Prefix:	mrns_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Monetary value of common stock authorized to be issued.

+ References

No definition available.

+ Details

Name:	mrns_CommonStockValueSharesAuthorized
Namespace Prefix:	mrns_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The aggregate offering price of shares to be issued under the equity distribution agreement.

+ References

No definition available.

+ Details

Name:	mrns_EquityDistributionAgreementThresholdOfferingPriceOfSharesToBeIssued
Namespace Prefix:	mrns_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Commissions paid on sale of stock as a percentage of gross sales price of shares sold.

+ References

No definition available.

+ Details

Name:	mrns_SaleOfStockCommissionPercentage
Namespace Prefix:	mrns_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of shares issued during the period under the equity distribution agreement.

+ References

No definition available.

+ Details

Name:	mrns_StockIssuedDuringPeriodSharesEquityDistributionAgreement
Namespace Prefix:	mrns_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

The cash inflow from the additional capital contribution to the entity.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 14
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=123570139&loc=d3e3255-108585

+ Details

Name:	us-gaap_ProceedsFromIssuanceOfCommonStock
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- 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

- Details

Name:	us-gaap_StatementEquityComponentsAxis=us-gaap_CommonStockMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_SubsidiarySaleOfStockAxis=mrns_EquityDistributionAgreement2017Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_SubsidiarySaleOfStockAxis=mrns_EquityDistributionAgreement2020Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Stockholders' Equity - Equity Distribution Agreement (Details) - USD ($) $ in Millions		1 Months Ended	12 Months Ended
	Jul. 09, 2020	Oct. 31, 2017	Dec. 31, 2020
Common Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Issuance of shares under equity distribution agreement (in shares)			78,807
2017 Equity Distribution Agreement
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Term of Equity Distribution Agreement		3 years
Value of common stock authorized under EDA		$ 50.0
2017 Equity Distribution Agreement \| Common Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Issuance of shares under equity distribution agreement (in shares)			78,807
Net proceeds from issuance of common stock			$ 0.5
2020 Equity Distribution Agreement \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock an aggregate offering price	$ 60.0
Sale of common stock, commission percentage	3.00%