| Document and Entity Information | Nov. 12, 2019 |
| Cover page. | |
| Document Type | 8-K |
| Document Period End Date | Nov. 12, 2019 |
| Entity Registrant Name | CARDIOVASCULAR SYSTEMS, INC. |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 000-52082 |
| Entity Tax Identification Number | 41-1698056 |
| Entity Address, Address Line One | 1225 Old Highway 8 Northwest |
| Entity Address, City or Town | St. Paul |
| Entity Address, State or Province | MN |
| Entity Address, Postal Zip Code | 55112-6416 |
| City Area Code | 651 |
| Local Phone Number | 259-1600 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| Title of 12(b) Security | Common Stock, One-tenth of One Cent ($0.001)Par Value Per Share |
| Trading Symbol | CSII |
| Security Exchange Name | NASDAQ |
| Entity Central Index Key | 0001180145 |
| Amendment Flag | false |
