Represents the tax exemption period for income tax rate.

No definition available.

Name:	cmcm_IncomeTaxExemptionPeriod
Namespace Prefix:	cmcm_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the statutory corporate income tax rate in the foreign jurisdiction.

+ References

No definition available.

+ Details

Name:	cmcm_IncomeTaxForeignStatutoryTaxRate
Namespace Prefix:	cmcm_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the statutory corporate income tax rate over the stated taxable income in the foreign jurisdiction.

+ References

No definition available.

+ Details

Name:	cmcm_IncomeTaxForeignStatutoryTaxRateOverStatedIncomeLevel
Namespace Prefix:	cmcm_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the preferential tax rate applicable to the entity under the preferential tax treatment.

+ References

No definition available.

+ Details

Name:	cmcm_IncomeTaxPreferentialTaxRate
Namespace Prefix:	cmcm_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the percentage by which the tax rate is reduced for the stated period following the initial exemption period.

+ References

No definition available.

+ Details

Name:	cmcm_IncomeTaxReductionPercentageFollowingExemptionPeriod
Namespace Prefix:	cmcm_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the period during which the entity is entitled for a specified percentage reduction in income tax following the initial exemption period from the first profitable year.

+ References

No definition available.

+ Details

Name:	cmcm_IncomeTaxReductionPeriod
Namespace Prefix:	cmcm_
Data Type:	xbrli:durationItemType
Balance Type:	na
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:	cmcm_IncomeTaxesLineItems
Namespace Prefix:	cmcm_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Taxable Losses

+ References

No definition available.

+ Details

Name:	cmcm_TaxableLosses
Namespace Prefix:	cmcm_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of unrecognized tax benefits pertaining to uncertain tax positions taken in tax returns net against deferred tax assets related to tax loss carryforwards.

+ References

No definition available.

+ Details

Name:	cmcm_UnrecognizedTaxBenefitsNetAgainstTaxLossCarryforwards
Namespace Prefix:	cmcm_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Represents the amount of unrecognized tax benefits presented in the other non-current liabilities line item in the consolidated balance sheets.

+ References

No definition available.

+ Details

Name:	cmcm_UnrecognizedTaxBenefitsNetConsolidatedBalanceSheet
Namespace Prefix:	cmcm_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Represents the withholding income tax rate for dividend paid to foreign tax resident investors.

+ References

No definition available.

+ Details

Name:	cmcm_WithholdingIncomeTaxRateForDividendPaidToForeignTaxResidentInvestors
Namespace Prefix:	cmcm_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Withholding income tax rate on dividends distributed by foreign invested enterprise.

+ References

No definition available.

+ Details

Name:	cmcm_WithholdingIncomeTaxRateOnDividendsDistributedByForeignInvestedEnterprise
Namespace Prefix:	cmcm_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Excess of issue price over par or stated value of the entity's capital stock and amounts received from other transactions involving the entity's stock or stockholders. Includes adjustments to additional paid in capital. Some examples of such adjustments include recording the issuance of debt with a beneficial conversion feature and certain tax consequences of equity instruments awarded to employees. Use this element for the aggregate amount of additional paid-in capital associated with common and preferred stock. For additional paid-in capital associated with only common stock, use the element additional paid in capital, common stock. For additional paid-in capital associated with only preferred stock, use the element additional paid in capital, preferred stock.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(30)(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- Definition

Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences and carryforwards.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32537-109319

+ Details

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

- Definition

Amount of deferred tax assets for which it is more likely than not that a tax benefit will not be realized.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32537-109319

+ Details

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

- Definition

Amount of deferred tax liability not recognized because of the exceptions to comprehensive recognition of deferred taxes related to undistributed earnings of domestic subsidiaries.

+ References

+ Details

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

- Definition

Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32687-109319

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB TOPIC 6.I)
-URI http://asc.fasb.org/extlink&oid=34349781&loc=d3e330036-122817

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 13
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32698-109319

+ Details

Name:	us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of income taxes from which a reporting entity is exempt or for which it will receive a reduction in income taxes as a result of the income tax holiday granted by the taxing jurisdiction.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SAB Topic 11.C)
-URI http://asc.fasb.org/extlink&oid=34349781&loc=d3e330215-122817

+ Details

Name:	us-gaap_IncomeTaxHolidayAggregateDollarAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Per share amount effect of the income tax benefit resulting from the income tax holidays granted by taxing jurisdictions.

+ References

+ Details

Name:	us-gaap_IncomeTaxHolidayIncomeTaxBenefitsPerShare
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

Tax year that remains open to examination under enacted tax laws, in CCYY format.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32718-109319

+ Details

Name:	us-gaap_OpenTaxYear
Namespace Prefix:	us-gaap_
Data Type:	xbrli:gYearItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of undistributed earnings of domestic subsidiaries or domestic joint ventures intended to be permanent.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=6424122&loc=d3e41874-109331

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (b)(c)
-URI http://asc.fasb.org/extlink&oid=6424122&loc=d3e41874-109331

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 25
-Paragraph 3
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=96869850&loc=d3e28200-109314

+ Details

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

- Definition

Amount of unrecognized tax benefits.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 15A
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=84230637&loc=SL6600010-109319

+ Details

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

- Definition

Amount of expense for penalties related to a tax position claimed or expected to be claimed in the tax return.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32718-109319

+ Details

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

- Definition

Amount of interest expense accrued for an underpayment of income taxes.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32718-109319

+ Details

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

- Definition

Amount of interest expense for an underpayment of income taxes.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32718-109319

+ Details

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

- Definition

The total amount of unrecognized tax benefits that, if recognized, would affect the effective tax rate.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 15A
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=84230637&loc=SL6600010-109319

+ Details

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

- Details

Name:	us-gaap_StatementScenarioAxis=us-gaap_ScenarioPlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementGeographicalAxis=country_US
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_StatementGeographicalAxis=stpr_CA
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementGeographicalAxis=country_HK
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

Name:	us-gaap_StatementGeographicalAxis=country_SG
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	cmcm_StatusForTaxabilityAxis=cmcm_DevelopmentExpansionIncentiveSchemeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementGeographicalAxis=country_JP
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_StatementGeographicalAxis=country_FR
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_StatementGeographicalAxis=country_CN
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_GainContingenciesByNatureAxis=us-gaap_ReductionInTaxesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ProductOrServiceAxis=cmcm_NewSoftwareDevelopmentEnterprisesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ProductOrServiceAxis=cmcm_HighNewTechnologyEnterpriseMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementGeographicalAxis=country_TW
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Income Taxes- Additional Information (Detail) ¥ / shares in Units, $ / shares in Units, ¥ in Thousands, $ in Thousands, ¥ in Millions				12 Months Ended
	Apr. 01, 2016 JPY (¥)	Apr. 01, 2015 JPY (¥)	Mar. 31, 2015 JPY (¥)	Jan. 01, 2018	Dec. 31, 2017 CNY (¥) ¥ / shares	Dec. 31, 2017 USD ($) $ / shares	Dec. 31, 2016 CNY (¥) ¥ / shares	Dec. 31, 2015 CNY (¥) ¥ / shares	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Income Taxes [Line Items]
Paid-in capital					¥ 2,644,043		¥ 2,725,675		$ 406,382
Total deferred tax assets before valuation allowances					129,625		131,724		19,923
Valuation allowances					71,983		41,388		11,064
Undistributed earnings					726,019		654,425		111,587
Taxable losses					406,398	$ 62,462
Unrecognized tax benefit					63,252		61,557	¥ 46,615	9,722	$ 9,461
Unrecognized tax benefit net against deferred tax loss carryforwards					29,629	4,554	43,934
Unrecognized tax benefit presented in the other non-current liabilities line item					33,623	5,168	17,623
Amount of unrecognized tax benefits that if recognized would impact the annual effective tax rate					33,623		13,228		5,168
Interest related to unrecognized tax benefits					5,226	803	3,489
Penalties related to unrecognized tax benefits					0	$ 0	0
Interest accrued related to unrecognized tax benefits					10,209		4,983		1,569
Scenario, Plan
Income Taxes [Line Items]
Statutory rate				21.00%
Maximum [Member]
Income Taxes [Line Items]
Unrecognized deferred income tax liabilities					72,602		65,442		11,159
Minimum [Member]
Income Taxes [Line Items]
Unrecognized deferred income tax liabilities					¥ 36,301		¥ 32,721		$ 5,579
UNITED STATES
Income Taxes [Line Items]
Taxable loss expiration Year					2036	2036
UNITED STATES \| Cheetah Mobile America, Mob Inc. and Live.me America
Income Taxes [Line Items]
Foreign statutory tax rate					35.00%	35.00%
CALIFORNIA \| Cheetah Mobile America, Mob Inc. and Live.me America
Income Taxes [Line Items]
Foreign statutory tax rate					8.84%	8.84%
HONG KONG \| Cheetah Technology
Income Taxes [Line Items]
Foreign statutory tax rate					16.50%	16.50%
HONG KONG \| HK Zoom
Income Taxes [Line Items]
Foreign statutory tax rate					16.50%	16.50%
HONG KONG \| Youloft HK
Income Taxes [Line Items]
Foreign statutory tax rate					16.50%	16.50%
HONG KONG \| Cheetah Information Hong Kong Live.me
Income Taxes [Line Items]
Foreign statutory tax rate					16.50%	16.50%
HONG KONG \| Cheetah Mobile Hong Kong
Income Taxes [Line Items]
Foreign statutory tax rate					16.50%	16.50%
SINGAPORE \| Cheetah Mobile Singapore
Income Taxes [Line Items]
Foreign statutory tax rate					17.00%	17.00%
Reduction in tax rate for stated period following the exemption period					5.00%	5.00%
SINGAPORE \| Cheetah Mobile Singapore \| Development Expansion Incentive Scheme
Income Taxes [Line Items]
Period for reduction in tax percentage					10 years	10 years
JAPAN \| Japan Kingsoft
Income Taxes [Line Items]
Foreign statutory tax rate	15.00%	15.00%	25.50%
Reduction in tax rate for stated period following the exemption period	23.40%	23.90%
Paid-in capital	¥ 8	¥ 8
Foreign statutory tax rate over stated taxable income level	23.40%
JAPAN \| Japan Kingsoft \| Maximum [Member]
Income Taxes [Line Items]
Paid-in capital	¥ 100	¥ 100
JAPAN \| Japan Kingsoft \| Minimum [Member]
Income Taxes [Line Items]
Paid-in capital			¥ 100
FRANCE \| Mob Partner and News Republic
Income Taxes [Line Items]
Foreign statutory tax rate					33.33%	33.33%
PRC
Income Taxes [Line Items]
Statutory rate					25.00%	25.00%	25.00%	25.00%
Withholding income tax rate for dividend paid to foreign tax resident investors (as a percent)					10.00%	10.00%
PRC \| Reduction in Taxes [Member]
Income Taxes [Line Items]
Withholding tax, Reduction					5.00%	5.00%
PRC \| Maximum [Member]
Income Taxes [Line Items]
Taxable loss expiration Year					2022	2022
PRC \| Minimum [Member]
Income Taxes [Line Items]
Taxable loss expiration Year					2018	2018
PRC \| New Software Development Enterprise
Income Taxes [Line Items]
Reduction in tax rate for stated period following the exemption period					50.00%	50.00%
Period for reduction in tax percentage					3 years	3 years
Exemption period for income tax					2 years	2 years
Income Tax Holiday, Aggregate Dollar Amount					¥ 67,934	$ 10,441	¥ 31,470	¥ 21,301
Income tax holiday, income tax benefits per share \| (per share)					¥ 0.0487	$ 0.0075	¥ 0.0227	¥ 0.0155
PRC \| HNTE
Income Taxes [Line Items]
Exemption period for income tax					3 years	3 years
Preferential tax rate					15.00%	15.00%
TAIWAN, PROVINCE OF CHINA \| Maximum [Member]
Income Taxes [Line Items]
Taxable loss expiration Year					2027	2027