v2.4.1.9

Fair Value of Financial Instruments (Contractual Maturity) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Mature within One Year	$ 52,014qlys_AvailableForSaleSecuritiesDebtAndEquityMaturitiesNextTwelveMonthsFairValue	$ 69,525qlys_AvailableForSaleSecuritiesDebtAndEquityMaturitiesNextTwelveMonthsFairValue
After One Year through Two Years	30,681qlys_AvailableForSaleSecuritiesDebtAndEquityMaturitiesYearOneThroughTwoFairValue	30,107qlys_AvailableForSaleSecuritiesDebtAndEquityMaturitiesYearOneThroughTwoFairValue
Over Two Years	8,767qlys_AvailableForSaleSecuritiesDebtAndEquityMaturitiesAfterYearTwoFairValue	5,501qlys_AvailableForSaleSecuritiesDebtAndEquityMaturitiesAfterYearTwoFairValue
Fair Value	91,462us-gaap_AvailableForSaleSecurities	105,133us-gaap_AvailableForSaleSecurities
Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Mature within One Year	5,999qlys_AvailableForSaleSecuritiesDebtAndEquityMaturitiesNextTwelveMonthsFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CommercialPaperMember	47,488qlys_AvailableForSaleSecuritiesDebtAndEquityMaturitiesNextTwelveMonthsFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CommercialPaperMember
After One Year through Two Years	0qlys_AvailableForSaleSecuritiesDebtAndEquityMaturitiesYearOneThroughTwoFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CommercialPaperMember	0qlys_AvailableForSaleSecuritiesDebtAndEquityMaturitiesYearOneThroughTwoFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CommercialPaperMember
Over Two Years	0qlys_AvailableForSaleSecuritiesDebtAndEquityMaturitiesAfterYearTwoFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CommercialPaperMember	0qlys_AvailableForSaleSecuritiesDebtAndEquityMaturitiesAfterYearTwoFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CommercialPaperMember
Fair Value	5,999us-gaap_AvailableForSaleSecurities / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CommercialPaperMember	47,488us-gaap_AvailableForSaleSecurities / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CommercialPaperMember
U.S. government agencies
Schedule of Available-for-sale Securities [Line Items]
Mature within One Year	33,577qlys_AvailableForSaleSecuritiesDebtAndEquityMaturitiesNextTwelveMonthsFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember	4,004qlys_AvailableForSaleSecuritiesDebtAndEquityMaturitiesNextTwelveMonthsFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember
After One Year through Two Years	20,255qlys_AvailableForSaleSecuritiesDebtAndEquityMaturitiesYearOneThroughTwoFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember	14,833qlys_AvailableForSaleSecuritiesDebtAndEquityMaturitiesYearOneThroughTwoFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember
Over Two Years	0qlys_AvailableForSaleSecuritiesDebtAndEquityMaturitiesAfterYearTwoFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember	0qlys_AvailableForSaleSecuritiesDebtAndEquityMaturitiesAfterYearTwoFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember
Fair Value	53,832us-gaap_AvailableForSaleSecurities / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember	18,837us-gaap_AvailableForSaleSecurities / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember
Municipal bonds
Schedule of Available-for-sale Securities [Line Items]
Mature within One Year		1,128qlys_AvailableForSaleSecuritiesDebtAndEquityMaturitiesNextTwelveMonthsFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MunicipalBondsMember
After One Year through Two Years		0qlys_AvailableForSaleSecuritiesDebtAndEquityMaturitiesYearOneThroughTwoFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MunicipalBondsMember
Over Two Years		0qlys_AvailableForSaleSecuritiesDebtAndEquityMaturitiesAfterYearTwoFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MunicipalBondsMember
Fair Value		1,128us-gaap_AvailableForSaleSecurities / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MunicipalBondsMember
Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Mature within One Year	12,438qlys_AvailableForSaleSecuritiesDebtAndEquityMaturitiesNextTwelveMonthsFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CorporateBondSecuritiesMember	16,905qlys_AvailableForSaleSecuritiesDebtAndEquityMaturitiesNextTwelveMonthsFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CorporateBondSecuritiesMember
After One Year through Two Years	3,099qlys_AvailableForSaleSecuritiesDebtAndEquityMaturitiesYearOneThroughTwoFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CorporateBondSecuritiesMember	15,274qlys_AvailableForSaleSecuritiesDebtAndEquityMaturitiesYearOneThroughTwoFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CorporateBondSecuritiesMember
Over Two Years	0qlys_AvailableForSaleSecuritiesDebtAndEquityMaturitiesAfterYearTwoFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CorporateBondSecuritiesMember	0qlys_AvailableForSaleSecuritiesDebtAndEquityMaturitiesAfterYearTwoFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CorporateBondSecuritiesMember
Fair Value	15,537us-gaap_AvailableForSaleSecurities / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CorporateBondSecuritiesMember	32,179us-gaap_AvailableForSaleSecurities / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CorporateBondSecuritiesMember
Asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Mature within One Year	0qlys_AvailableForSaleSecuritiesDebtAndEquityMaturitiesNextTwelveMonthsFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_AssetBackedSecuritiesMember	0qlys_AvailableForSaleSecuritiesDebtAndEquityMaturitiesNextTwelveMonthsFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_AssetBackedSecuritiesMember
After One Year through Two Years	7,327qlys_AvailableForSaleSecuritiesDebtAndEquityMaturitiesYearOneThroughTwoFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_AssetBackedSecuritiesMember	0qlys_AvailableForSaleSecuritiesDebtAndEquityMaturitiesYearOneThroughTwoFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_AssetBackedSecuritiesMember
Over Two Years	8,767qlys_AvailableForSaleSecuritiesDebtAndEquityMaturitiesAfterYearTwoFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_AssetBackedSecuritiesMember	5,501qlys_AvailableForSaleSecuritiesDebtAndEquityMaturitiesAfterYearTwoFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_AssetBackedSecuritiesMember
Fair Value	$ 16,094us-gaap_AvailableForSaleSecurities / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_AssetBackedSecuritiesMember	$ 5,501us-gaap_AvailableForSaleSecurities / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_AssetBackedSecuritiesMember

X

- Definition

Available-for-sale Securities, Debt and Equity Maturities, After Year Two, Fair Value

+ References

No definition available.

+ Details

Name:	qlys_AvailableForSaleSecuritiesDebtAndEquityMaturitiesAfterYearTwoFairValue
Namespace Prefix:	qlys_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

Available-for-sale Securities, Debt and Equity Maturities, Next Twelve Months, Fair Value

+ References

No definition available.

+ Details

Name:	qlys_AvailableForSaleSecuritiesDebtAndEquityMaturitiesNextTwelveMonthsFairValue
Namespace Prefix:	qlys_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

Available-for-sale Securities, Debt and Equity Maturities, Year One through Two, Fair Value

+ References

No definition available.

+ Details

Name:	qlys_AvailableForSaleSecuritiesDebtAndEquityMaturitiesYearOneThroughTwoFairValue
Namespace Prefix:	qlys_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 25

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=28360136&loc=d3e22054-111558



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 5

-Subparagraph (aa)

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563



Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26610-111562

+ Details

Name:	us-gaap_AvailableForSaleSecurities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Details

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

X

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_AssetBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_CommercialPaperMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_CorporateBondSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_MunicipalBondsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_USGovernmentAgenciesDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: