Document and Entity Information - shares	9 Months Ended
	Mar. 31, 2020	May 01, 2020
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Transition Report	false
Amendment Flag	false
Document Period End Date	Mar. 31, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q3
Entity File Number	000-52082
Entity Registrant Name	CARDIOVASCULAR SYSTEMS, INC.
Entity Incorporation, State or Country Code	DE
Entity Central Index Key	0001180145
Current Fiscal Year End Date	--06-30
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
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell 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 Common Stock, Shares Outstanding		35,274,437