| Document and Entity Information | Dec. 10, 2020 |
| Cover [Abstract] | |
| Entity Registrant Name | BIODESIX INC |
| Amendment Flag | false |
| Entity Central Index Key | 0001439725 |
| Document Type | 8-K |
| Document Period End Date | Dec. 10, 2020 |
| Entity Incorporation State Country Code | DE |
| Entity File Number | 001-39659 |
| Entity Tax Identification Number | 20-3986492 |
| Entity Address, Address Line One | 2970 Wilderness Place |
| Entity Address, Address Line Two | Suite 100 |
| Entity Address, City or Town | Boulder |
| Entity Address, State or Province | CO |
| Entity Address, Postal Zip Code | 80301 |
| City Area Code | (303) |
| Local Phone Number | 417-0500 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Security 12b Title | Common Stock, par value of $0.001 per share |
| Trading Symbol | BDSX |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | true |
| Entity Ex Transition Period | false |
