Summary of Significant Accounting Policies - Leases - Gross Difference (Details) $ in Thousands	Dec. 31, 2020 USD ($)
Leases
Total lease payments	$ 57,225
Less interest	(1,349)
Present value of lease liabilities	$ 55,876

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

No definition available.

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