Income Taxes - Additional Information (Details)	3 Months Ended
Mar. 31, 2019
Income Tax Disclosure [Abstract]
Minimum percentage of likelihood of realization of tax benefits	50.00%

Percentage of likelihood of realization of recognized tax benefit, minimum.

No definition available.

Name:	myok_PercentageOfLikelihoodOfRealizationOfRecognizedTaxBenefitMinimum
Namespace Prefix:	myok_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration