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Income Taxes- Additional Information (Detail) ¥ / shares in Units, $ / shares in Units, ¥ in Thousands, $ in Thousands, ¥ in Millions |  |  |  | 12 Months Ended |  |
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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 |  |  |  |

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- 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
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