| Document and Entity Information | Mar. 22, 2021 | Apr. 01, 2020 |
| Cover [Abstract] | ||
| Document Type | 8-K | |
| Document Period End Date | Mar. 22, 2021 | |
| 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 |
