v3.25.0.1

Cover - USD ($) $ in Millions	12 Months Ended
Cover - USD ($) $ in Millions	Dec. 31, 2024	Feb. 11, 2025	Jun. 30, 2024
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2024
Current Fiscal Year End Date	--12-31
Document Transition Report	false
Entity File Number	001-35662
Entity Registrant Name	QUALYS, INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	77-0534145
Entity Address, Address Line One	919 E. Hillsdale Boulevard, 4th Floor
Entity Address, City or Town	Foster City
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94404
City Area Code	650
Local Phone Number	801-6100
Title of 12(b) Security	Common stock, $0.001 par value per share
Trading Symbol	QLYS
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
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
ICFR Auditor Attestation Flag	true
Document Financial Statement Error Correction	false
Entity Shell Company	false
Entity Public Float			$ 3,908
Entity Common Stock, Shares Outstanding		36,477,672
Documents Incorporated by Reference	Portions of the registrant's Proxy Statement for its 2025 Annual Meeting of Stockholders are incorporated by reference in Part III of this Annual Report on Form 10-K where indicated. Such proxy statement will be filed with the Securities and Exchange Commission within 120 days of the registrant's fiscal year ended December 31, 2024.
Entity Central Index Key	0001107843
Document Fiscal Year Focus	2024
Document Fiscal Period Focus	FY
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QUALYS, INC. 10-K