Capital Leased Assets, Interest Rate

No definition available.

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Namespace Prefix:	qlys_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Lease, Expense

+ References

No definition available.

+ Details

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Namespace Prefix:	qlys_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Lease, Office Building, Square Feet

+ References

No definition available.

+ Details

Name:	qlys_LeaseOfficeBuildingSquareFeet
Namespace Prefix:	qlys_
Data Type:	num:areaItemType
Balance Type:	na
Period Type:	duration

- Definition

Present value of lessee's discounted obligation for lease payments from finance lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=77888426&loc=SL77918701-209980

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=77888419&loc=SL77918627-209977

+ Details

Name:	us-gaap_FinanceLeaseLiability
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of rent expense incurred for leased assets, including but not limited to, furniture and equipment, that is not directly or indirectly associated with the manufacture, sale or creation of a product or product line.

+ References

No definition available.

+ Details

Name:	us-gaap_LeaseAndRentalExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_OperatingLeasedAssetsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of increase in right-of-use asset obtained in exchange for operating lease liability.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 55
-Paragraph 53
-URI http://asc.fasb.org/extlink&oid=77888399&loc=SL77918982-209971

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (g)(2)
-URI http://asc.fasb.org/extlink&oid=77888426&loc=SL77918686-209980

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	dei_LegalEntityAxis=qlys_PuneIndiaDomain
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Commitments and Contingencies (Additional Information) (Details) ft² in Thousands, $ in Thousands		1 Months Ended	3 Months Ended	12 Months Ended
	Oct. 01, 2019 USD ($)	Jan. 31, 2018	Dec. 31, 2019 USD ($) ft²	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Jan. 01, 2018 USD ($)
Operating Leased Assets [Line Items]
Lease, Expense				$ 13,900	$ 9,900
Finance Lease, Liability			$ 178	$ 178			$ 3,500
Capital Leased Assets, Interest Rate		5.00%
Lease, Office Building, Square Feet \| ft²			282,000
Rent expense						$ 9,600
Pune, India [Domain]
Operating Leased Assets [Line Items]
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	$ 14,700