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Summary of Significant Accounting Policies - Income Taxes (Details)	6 Months Ended
	Jun. 30, 2017
Income Taxes
Valuation allowance on deferred tax assets (as a percent)	100.00%

X

- Definition

The percentage of valuation allowance on the deferred tax assets.

+ References

No definition available.

+ Details

Name:	mdgl_DeferredTaxAssetsPercentageOfValuationAllowance
Namespace Prefix:	mdgl_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

X

- References

No definition available.

+ Details

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