Related Party Transactions (Details) - USD ($)	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015
Related Party Transactions
Interest expense incurred on debt from related parties	$ 1,213,000	$ 3,603,000
Former CEO \| Consulting agreement
Related Party Transactions
Period of notice for termination of consulting agreement	15 days
Consulting fees paid	$ 93,000	$ 165,000

Represents the period of of notice to be provided by the reporting entity for terminating the consulting agreement.

No definition available.

Name:	mdgl_RelatedPartyTransactionPeriodOfPriorNoticeForTerminationOfAgreement
Namespace Prefix:	mdgl_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of interest expense incurred on a debt or other obligation to related party.

+ References

No definition available.

+ Details

Name:	us-gaap_InterestExpenseRelatedParty
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Expenses recognized resulting from transactions (excluding transactions that are eliminated in consolidated or combined financial statements) with related party.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=mdgl_FormerChiefExecutiveOfficerMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RelatedPartyTransactionAxis=mdgl_ConsultingAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: