| Document and Entity Information | May 11, 2020 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | May 11, 2020 |
| Entity Registrant Name | MYOKARDIA, INC. |
| Entity Central Index Key | 0001552451 |
| Entity Emerging Growth Company | false |
| Entity File Number | 001-37609 |
| Entity Incorporation, State or Country Code | DE |
| Entity Tax Identification Number | 44-5500552 |
| Entity Address, Address Line One | 1000 Sierra Point Parkway |
| Entity Address, City or Town | Brisbane |
| Entity Address, State or Province | CA |
| Entity Address, Postal Zip Code | 94005 |
| City Area Code | (650) |
| Local Phone Number | 741-0900 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Security 12b Title | Common Stock, par value $0.0001 |
| Trading Symbol | MYOK |
| Security Exchange Name | NASDAQ |
