Summary of Significant Accounting Policies - Health Care Reform (Details) $ in Millions	12 Months Ended
Dec. 31, 2020 USD ($)
Summary of Significant Accounting Policies
HIF fees	$ 36.2
HIF fees, continuing operations	$ 12.4

Affordable Care Act, Fiscal Year Annual Fees Paid During Period, Continuing Operations

No definition available.

Name:	mgln_AffordableCareActFiscalYearAnnualFeesPaidDuringPeriodContinuingOperations
Namespace Prefix:	mgln_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration