Stockholders' Equity (Deficit) - Common Stock (Details)	12 Months Ended
Dec. 31, 2019 Vote
Stockholders' Equity Note [Abstract]
Number of votes per share that common stockholders are entitled to receive	1

Represents the number of votes per share that common stockholders are entitled to receive.

No definition available.

Name:	mdgl_CommonStockVotingRightsNumber
Namespace Prefix:	mdgl_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration