Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Jun. 30, 2020	Aug. 14, 2020	Dec. 31, 2019
Document and Entity Information [Abstract]
Document Type	10-K
Document Annual Report	true
Document Transition Report	false
Document Period End Date	Jun. 30, 2020
Entity File Number	000-52082
Entity Registrant Name	CARDIOVASCULAR SYSTEMS, INC.
Entity Incorporation, State or Country Code	DE
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
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 Well-known Seasoned Issuer	Yes
Entity Interactive Data Current	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
ICFR Auditor Attestation Flag	true
Entity Small Business	false
Entity Current Reporting Status	Yes
Entity Shell Company	false
Entity Public Float			$ 1,665.3
Entity Common Stock, Shares Outstanding		39,669,083
Entity Central Index Key	0001180145
Amendment Flag	false
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Current Fiscal Year End Date	--06-30
Entity Emerging Growth Company	false