Amount incurred towards exit fees of term loan.

No definition available.

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

- Definition

The additional borrowing capacity available under the credit agreement, subject to certain milestone events.

+ References

No definition available.

+ Details

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

- Definition

The amount points added to the commitment fees on the debt instrument.

+ References

No definition available.

+ Details

Name:	mrns_DebtInstrumentCommitmentFee
Namespace Prefix:	mrns_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Period for which the commitment fees accrues until the applicable tranche is either funded or terminated, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

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

- Definition

The exit fee expressed as a percentage of all principal repaid, whether as a mandatory prepayment, voluntary prepayment, or a scheduled repayment.

+ References

No definition available.

+ Details

Name:	mrns_DebtInstrumentExitFeePercentage
Namespace Prefix:	mrns_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The minimum requirement that must be met on gross proceeds from a sublicense in determining availability of funding per the credit agreement.

+ References

No definition available.

+ Details

Name:	mrns_DebtInstrumentFundingAvailableGrossProceedsFromSublicenseMinimum
Namespace Prefix:	mrns_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The minimum requirement that must be met on net proceeds from a sublicense in determining availability of funding per the credit agreement.

+ References

No definition available.

+ Details

Name:	mrns_DebtInstrumentFundingAvailableNetProceedsFromSublicenseMinimum
Namespace Prefix:	mrns_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Percentage of periodic principal payment.

+ References

No definition available.

+ Details

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

- Definition

Upfront fee expressed as a percentage of the aggregate principal amount borrowed at that time.

+ References

No definition available.

+ Details

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

- Definition

Amount of minimum liquidity to be maintained in cash.

+ References

No definition available.

+ Details

Name:	mrns_MinimumCashLiquidityValue
Namespace Prefix:	mrns_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Number of tranches within term loan for notes payable.

+ References

No definition available.

+ Details

Name:	mrns_NumberOfTranches
Namespace Prefix:	mrns_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

The prepayment premium expressed as a percentage of the principal prepaid.

+ References

No definition available.

+ Details

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

- Definition

Amount of amortization expense attributable to debt issuance costs.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=126954810&loc=d3e3602-108585

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03(8))
-URI https://asc.fasb.org/extlink&oid=126953954&loc=SL114868664-224227

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 1F
-Subparagraph (b)(2)
-URI https://asc.fasb.org/extlink&oid=123466505&loc=SL123495355-112611

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 3
-URI https://asc.fasb.org/extlink&oid=124435984&loc=d3e28555-108399

+ Details

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

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 1B
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=123466505&loc=SL123495323-112611

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI https://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
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_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentTerm
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount, before accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 3
-URI https://asc.fasb.org/extlink&oid=124435984&loc=d3e28555-108399

+ Details

Name:	us-gaap_DeferredFinanceCostsGross
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 1D
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=123466505&loc=SL123495340-112611

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 3
-URI https://asc.fasb.org/extlink&oid=124435984&loc=d3e28555-108399

+ Details

Name:	us-gaap_DeferredFinanceCostsNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of the cost of borrowed funds accounted for as interest expense.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=6450988&loc=d3e26243-108391

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 3
-URI https://asc.fasb.org/extlink&oid=124435984&loc=d3e28555-108399

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 22
-Subparagraph (d)
-URI https://asc.fasb.org/extlink&oid=126901519&loc=d3e8736-108599

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (210.5-03(11))
-URI https://asc.fasb.org/extlink&oid=126953954&loc=SL114868664-224227

Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.9)
-URI https://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260

+ Details

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

- Definition

Amount of the cost of borrowed funds accounted for as interest expense for debt.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 6
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=123466204&loc=SL6036836-161870

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.8)
-URI https://asc.fasb.org/extlink&oid=126953954&loc=SL114868664-224227

Reference 3: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 55
-Paragraph 69F
-URI https://asc.fasb.org/extlink&oid=123466577&loc=SL123495745-112612

Reference 4: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 55
-Paragraph 69E
-URI https://asc.fasb.org/extlink&oid=123466577&loc=SL123495743-112612

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 1F
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=123466505&loc=SL123495355-112611

+ Details

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

- Definition

The fee, expressed as a percentage of the line of credit facility, for the line of credit facility regardless of whether the facility has been used.

+ References

No definition available.

+ Details

Name:	us-gaap_LineOfCreditFacilityCommitmentFeePercentage
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ 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 210.5-02.19(b),22(b))
-URI https://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

Name:	us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of cash inflow from contractual arrangement with the lender, including but not limited to, letter of credit, standby letter of credit and revolving credit arrangements.

+ 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 (b)
-URI https://asc.fasb.org/extlink&oid=126954810&loc=d3e3255-108585

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(f))
-URI https://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690

+ Details

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

- Details

Name:	us-gaap_LineOfCreditFacilityAxis=mrns_OaktreeCapitalManagementLpCreditAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	srt_StatementScenarioAxis=mrns_PeriodOfFundingOfTrancheBTermLoanTillMaturityOfTermLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementScenarioAxis=mrns_ScenarioOfPrepaymentOnOrBeforeMay112023Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementScenarioAxis=mrns_ScenarioOfPrepaymentOccursBetweenMay112023ToMay112024Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementScenarioAxis=mrns_ScenarioOfPrepaymentBetweenMay112024ToMay112025Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementScenarioAxis=mrns_ScenarioOfPrepaymentAfterMay112025Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=mrns_TermLoansTranche1Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=mrns_TermLoansTranche2Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=mrns_TermLoanTrancheBMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=mrns_TermLoanTrancheCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Notes Payable - Narratives (Details) $ in Thousands		1 Months Ended			3 Months Ended
Notes Payable - Narratives (Details) $ in Thousands	May 11, 2021 USD ($) tranche	Mar. 31, 2022 USD ($)	Sep. 30, 2021 USD ($)	May 31, 2021 USD ($)	Mar. 31, 2023 USD ($)	Mar. 31, 2022 USD ($)	Oct. 31, 2022	Oct. 27, 2022 USD ($)	Sep. 30, 2022
Notes Payable
Contractual exit fee					$ 2,003
Interest expense					4,147	$ 1,692
Amortization of debt issuance costs					480	282
Oaktree Capital Management LP Credit Agreement
Notes Payable
Term of loan facility	5 years
Maximum borrowing capacity available under the credit agreement	$ 100,000
Number of tranches \| tranche	4
Proceeds from line of credit	$ 15,000	$ 30,000	$ 30,000
Additional borrowing capacity available, subject to certain milestone events	$ 25,000
Accrued interest rate (as a percent)	11.50%
Percentage of periodic principal payment	5.00%
Upfront fee (as a percent)	2.00%
Commitment fee (as a percent)	0.75%
Commitment fee accrual period	120 days
Debt issuance costs								$ 500
Debt issuance costs	$ 4,400	1,800	1,200			1,800
Contractual exit fee	$ 300		600
Interest expense					2,600
Interest on term loan					2,100
Amortization of debt issuance costs					$ 500
Exit fee, percentage	2.67%						2.67%	2.00%	2.00%
Oaktree Capital Management LP Credit Agreement \| Maximum
Notes Payable
Contractual exit fee		600				$ 600
Oaktree Capital Management LP Credit Agreement \| Funding date of the tranche B term loans until the maturity of the Term Loans
Notes Payable
Minimum liquidity to be maintained	$ 15,000
Oaktree Capital Management LP Credit Agreement \| Scenario Of Prepayment On Or Before May 11, 2023
Notes Payable
Prepayment premium (as a percent)	4.00%
Oaktree Capital Management LP Credit Agreement \| Scenario Of Prepayment Occurs Between May 11, 2023 To May 11, 2024
Notes Payable
Prepayment premium (as a percent)	4.00%
Oaktree Capital Management LP Credit Agreement \| Scenario Of Prepayment Between May 11, 2024 To May 11, 2025
Notes Payable
Prepayment premium (as a percent)	2.00%
Oaktree Capital Management LP Credit Agreement \| Scenario Of Prepayment After May 11, 2025
Notes Payable
Prepayment premium (as a percent)	0.00%
Oaktree Capital Management LP Credit Agreement \| Term Loans Tranche A-1
Notes Payable
Proceeds from line of credit				$ 15,000
Oaktree Capital Management LP Credit Agreement \| Term Loans Tranche A-2
Notes Payable
Proceeds from line of credit			$ 30,000
Oaktree Capital Management LP Credit Agreement \| Term Loan Tranche B
Notes Payable
Proceeds from line of credit		30,000
Oaktree Capital Management LP Credit Agreement \| Term Loan Tranche B \| Maximum
Notes Payable
Commitment fees		$ 100
Oaktree Capital Management LP Credit Agreement \| Term Loan Tranche C
Notes Payable
Additional borrowing capacity available, subject to certain milestone events	$ 25,000
Gross proceeds from sublicense, minimum	40,000
Net proceeds from sublicense, minimum	$ 36,000