Summary of Significant Accounting Policies - Leases - Maturity Dates (Details) $ in Thousands	Dec. 31, 2020 USD ($)
Leases
2020	$ 19,535
2021	14,883
2022	10,349
2023	8,557
2024	3,228
2025 and beyond	673
Total lease payments	$ 57,225

Amount of lessee's undiscounted obligation for lease payments for operating and finance leases.

No definition available.

Name:	mgln_LeaseLiabilityPaymentsDue
Namespace Prefix:	mgln_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of lessee's undiscounted obligation for lease payments for operating and finance lease, due after fifth fiscal year following latest fiscal year.

+ References

No definition available.

+ Details

Name:	mgln_LeaseLiabilityPaymentsDueAfterYearFive
Namespace Prefix:	mgln_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Lease Liability, Payments, Due Next Twelve Months

+ References

No definition available.

+ Details

Name:	mgln_LeaseLiabilityPaymentsDueNextTwelveMonths
Namespace Prefix:	mgln_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of lessee's undiscounted obligation for lease payments for operating and finance lease, due in fifth fiscal year following latest fiscal year.

+ References

No definition available.

+ Details

Name:	mgln_LeaseLiabilityPaymentsDueYearFive
Namespace Prefix:	mgln_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of lessee's undiscounted obligation for lease payments for operating and finance lease, due in fourth fiscal year following latest fiscal year.

+ References

No definition available.

+ Details

Name:	mgln_LeaseLiabilityPaymentsDueYearFour
Namespace Prefix:	mgln_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of lessee's undiscounted obligation for lease payments for operating and finance lease, due in third fiscal year following latest fiscal year.

+ References

No definition available.

+ Details

Name:	mgln_LeaseLiabilityPaymentsDueYearThree
Namespace Prefix:	mgln_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of lessee's undiscounted obligation for lease payments for operating and finance lease, due in second fiscal year following latest fiscal year.

+ References

No definition available.

+ Details

Name:	mgln_LeaseLiabilityPaymentsDueYearTwo
Namespace Prefix:	mgln_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- References

No definition available.

+ Details

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