Percentage points added to the reference rate to compute the variable rate on the debt instrument.

No definition available.

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(2))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)(2)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
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 http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- Definition

The fee, expressed as a percentage of the line of credit facility, for available but unused credit capacity under the credit facility.

+ References

No definition available.

+ Details

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

- Definition

Weighted average interest rate of long-term debt outstanding calculated over time.

+ References

No definition available.

+ Details

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

- Definition

The cash outflow for debt initially having maturity due after one year or beyond the normal operating cycle, if longer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 15
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3291-108585

+ Details

Name:	us-gaap_RepaymentsOfLongTermDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_UnsecuredDebtMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=mgln_CreditAgreement2017Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=mgln_CreditAgreement2017SeniorUnsecuredRevolvingCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=mgln_CreditAgreement2017SeniorUnsecuredTermLoanFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_PrimeRateMember
Namespace Prefix:
Data Type:	na
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Period Type:

- Details

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Data Type:	na
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- Details

Name:	us-gaap_VariableRateAxis=mgln_DebtInstrumentVariableRateBaseOneMonthEurodollarMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=mgln_DebtInstrumentVariableRateEurodollarRateForSelectedInterestPeriodMember
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General - Long-Term Debt, Finance Lease and Deferred Financing Obligations - Credit Agreement - General Information (Details) - USD ($) $ in Millions				1 Months Ended	3 Months Ended
	Aug. 13, 2018	Aug. 12, 2018	Sep. 22, 2017	Aug. 31, 2019	Mar. 31, 2020
Debt
Voluntary term loan repayments				$ 30.0
Unsecured Debt \| 2017 Credit Agreement
Debt
Debt instrument, maturity date	Sep. 22, 2023	Sep. 22, 2022	Sep. 22, 2022		Sep. 22, 2023
Unsecured Debt \| 2017 Credit Agreement, senior unsecured revolving credit facility
Debt
Maximum borrowing capacity			$ 400.0
Commitment commission (as a percent)					0.20%
Weighted average interest rate (as a percent)					3.6928%
Unsecured Debt \| 2017 Credit Agreement, senior unsecured term loan facility
Debt
Maximum borrowing capacity			$ 350.0
Unsecured Debt \| 2017 Credit Agreement, senior unsecured term loan facility \| Prime rate
Debt
Basis spread on variable rate (as a percent)			0.50%
Unsecured Debt \| 2017 Credit Agreement, senior unsecured term loan facility \| Federal Funds Rate
Debt
Basis spread on variable rate (as a percent)			0.50%
Unsecured Debt \| 2017 Credit Agreement, senior unsecured term loan facility \| Eurodollar rate for one month
Debt
Basis spread on variable rate (as a percent)			1.00%
Unsecured Debt \| 2017 Credit Agreement, senior unsecured term loan facility \| Eurodollar rate for selected interest period
Debt
Basis spread on variable rate (as a percent)			1.50%