Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Registrant Name

dei_EntityRegistrantName

FIDELITY ADVISOR SERIES VIII

Prospectus Date

rr_ProspectusDate

Dec. 30, 2014

A T B C | Fidelity Advisor Value Leaders Fund

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

rr_RiskReturnHeading

Fund Summary

Fund/Class:
Fidelity Advisor^® Value Leaders Fund /A, T, B, C

Objective [Heading]

rr_ObjectiveHeading

Investment Objective

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

The fund seeks capital appreciation.

Expense [Heading]

rr_ExpenseHeading

Fee Table

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

The following table describes the fees and expenses that may be incurred when you buy and hold shares of the fund.

You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in the fund or certain other Fidelity funds. More information about these and other discounts is available from your investment professional and in the Fund Distribution section beginning on page (Click Here) of the prospectus.

Shareholder Fees Caption [Text]

rr_ShareholderFeesCaption

Shareholder fees
(fees paid directly from your investment)

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

Annual operating expenses
(expenses that you pay each year as a % of the value of your investment)

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover

Portfolio Turnover [Text Block]

rr_PortfolioTurnoverTextBlock

The fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when fund shares are held in a taxable account. These costs, which are not reflected in annual operating expenses or in the example, affect the fund's performance. During the most recent fiscal year, the fund's portfolio turnover rate was 182% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

182.00%

Expense Breakpoint Discounts [Text]

rr_ExpenseBreakpointDiscounts

You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in the fund or certain other Fidelity funds.

Expense Breakpoint, Minimum Investment Required [Amount]

rr_ExpenseBreakpointMinimumInvestmentRequiredAmount

50,000

Expenses Not Correlated to Ratio Due to Acquired Fund Fees [Text]

rr_ExpensesNotCorrelatedToRatioDueToAcquiredFundFees

Differs from the ratios of expenses to average net assets in the Financial Highlights section of the prospectus because of acquired fund fees and expenses.

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

This example helps compare the cost of investing in the fund with the cost of investing in other funds.

Let's say, hypothetically, that the annual return for shares of the fund is 5% and that your shareholder fees and the annual operating expenses for shares of the fund are exactly as described in the fee table. This example illustrates the effect of fees and expenses, but is not meant to suggest actual or expected fees and expenses or returns, all of which may vary. For every $10,000 you invested, here's how much you would pay in total expenses if you sell all of your shares at the end of each time period indicated and if you hold your shares:

Expense Example by, Year, Caption [Text]

rr_ExpenseExampleByYearCaption

Sell All Shares

Expense Example, No Redemption, By Year, Caption [Text]

rr_ExpenseExampleNoRedemptionByYearCaption

Hold Shares

Strategy [Heading]

rr_StrategyHeading

Principal Investment Strategies

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

• Normally investing primarily in common stocks of well-known and established companies.
• Normally investing at least 80% of assets in blue chip companies (companies whose stock is included in the S&P 500^® Index or the Dow Jones Industrial Average℠ (DJIA℠), and companies with market capitalizations of at least $1 billion if not included in either index).
• Investing in securities of companies that Fidelity Management & Research Company (FMR) believes are undervalued in the marketplace in relation to factors such as assets, sales, earnings, growth potential, or cash flow, or in relation to securities of other companies in the same industry (stocks of these companies are often called "value" stocks).
• Investing in securities of domestic and foreign issuers.
• Using fundamental analysis of factors such as each issuer's financial condition and industry position, as well as market and economic conditions, to select investments.

Risk [Heading]

rr_RiskHeading

Principal Investment Risks

Risk Narrative [Text Block]

rr_RiskNarrativeTextBlock

• Stock Market Volatility. Stock markets are volatile and can decline significantly in response to adverse issuer, political, regulatory, market, or economic developments. Different parts of the market, including different market sectors, and different types of securities can react differently to these developments.
• Foreign Exposure. Foreign markets can be more volatile than the U.S. market due to increased risks of adverse issuer, political, regulatory, market, or economic developments and can perform differently from the U.S. market.
• Issuer-Specific Changes. The value of an individual security or particular type of security can be more volatile than, and can perform differently from, the market as a whole.
• "Value" Investing. "Value" stocks can perform differently from the market as a whole and other types of stocks and can continue to be undervalued by the market for long periods of time.

An investment in the fund is not a deposit of a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. You could lose money by investing in the fund.

Risk Lose Money [Text]

rr_RiskLoseMoney

You could lose money by investing in the fund.

Risk Not Insured Depository Institution [Text]

rr_RiskNotInsuredDepositoryInstitution

An investment in the fund is not a deposit of a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Bar Chart and Performance Table [Heading]

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Performance

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

The following information is intended to help you understand the risks of investing in the fund. The information illustrates the changes in the performance of the fund's shares from year to year and compares the performance of the fund's shares to the performance of a securities market index over various periods of time. The index description appears in the Additional Index Information section of the prospectus. Past performance (before and after taxes) is not an indication of future performance.

Visit www.advisor.fidelity.com for updated return information.

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The information illustrates the changes in the performance of the fund's shares from year to year and compares the performance of the fund's shares to the performance of a securities market index over various periods of time.

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

www.advisor.fidelity.com

Performance Past Does Not Indicate Future [Text]

rr_PerformancePastDoesNotIndicateFuture

Past performance (before and after taxes) is not an indication of future performance.

Bar Chart [Heading]

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Year-by-Year Returns

Bar Chart Does Not Reflect Sales Loads [Text]

rr_BarChartDoesNotReflectSalesLoads

The returns in the bar chart do not reflect any applicable sales charges; if sales charges were reflected, returns would be lower than those shown.

Calendar Years

Bar Chart Closing [Text Block]

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During the periods shown in the chart for Class A:	Returns	Quarter ended
Highest Quarter Return	19.83%	September 30, 2009
Lowest Quarter Return	-25.37%	December 31, 2008
Year-to-Date Return	4.58%	September 30, 2014

Performance Table Heading

rr_PerformanceTableHeading

Average Annual Returns

Performance Table Does Reflect Sales Loads

rr_PerformanceTableDoesReflectSalesLoads

Unlike the returns in the bar chart, the returns in the table reflect the maximum applicable sales charges.

Performance Table Uses Highest Federal Rate

rr_PerformanceTableUsesHighestFederalRate

After-tax returns are calculated using the historical highest individual federal marginal income tax rates, but do not reflect the impact of state or local taxes.

Performance Table Not Relevant to Tax Deferred

rr_PerformanceTableNotRelevantToTaxDeferred

The after-tax returns shown are not relevant if you hold your shares in a retirement account or in another tax-deferred arrangement.

Performance Table One Class of after Tax Shown [Text]

rr_PerformanceTableOneClassOfAfterTaxShown

After-tax returns for Class A are shown in the table below and after-tax returns for other classes will vary.

Performance Table Narrative

rr_PerformanceTableNarrativeTextBlock

Unlike the returns in the bar chart, the returns in the table reflect the maximum applicable sales charges. After-tax returns are calculated using the historical highest individual federal marginal income tax rates, but do not reflect the impact of state or local taxes. After-tax returns for Class A are shown in the table below and after-tax returns for other classes will vary. Actual after-tax returns may differ depending on your individual circumstances. The after-tax returns shown are not relevant if you hold your shares in a retirement account or in another tax-deferred arrangement.

For the periods ended
December 31, 2013

A T B C | Fidelity Advisor Value Leaders Fund | Class A

Risk/Return:

rr_RiskReturnAbstract

Maximum sales charge (load) on purchases (as a % of offering price)

rr_MaximumCumulativeSalesChargeOverOfferingPrice

5.75%

Maximum contingent deferred sales charge (as a % of the lesser of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

^[1]

Management fee (fluctuates based on the fund's performance relative to a securities market index)

rr_ManagementFeesOverAssets

0.36%

Distribution and/or Service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other expenses

rr_OtherExpensesOverAssets

0.69%

Acquired fund fees and expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.08%

Total annual operating expenses

rr_ExpensesOverAssets

1.38%

^[2]

Expenses Deferred Charges [Text Block]

rr_ExpensesDeferredChargesTextBlock

Class A and Class T purchases of $1 million or more will not be subject to a front-end sales charge. Such Class A and Class T purchases may be subject, upon redemption, to a contingent deferred sales charge (CDSC) of 1.00% or 0.25%, respectively.

1 year

rr_ExpenseExampleYear01

707

3 years

rr_ExpenseExampleYear03

987

5 years

rr_ExpenseExampleYear05

1,287

10 years

rr_ExpenseExampleYear10

2,137

1 year

rr_ExpenseExampleNoRedemptionYear01

707

3 years

rr_ExpenseExampleNoRedemptionYear03

987

5 years

rr_ExpenseExampleNoRedemptionYear05

1,287

10 years

rr_ExpenseExampleNoRedemptionYear10

2,137

2004

rr_AnnualReturn2004

14.25%

2005

rr_AnnualReturn2005

9.83%

2006

rr_AnnualReturn2006

15.00%

2007

rr_AnnualReturn2007

3.97%

2008

rr_AnnualReturn2008

(45.20%)

2009

rr_AnnualReturn2009

27.38%

2010

rr_AnnualReturn2010

9.58%

2011

rr_AnnualReturn2011

(8.00%)

2012

rr_AnnualReturn2012

13.66%

2013

rr_AnnualReturn2013

34.59%

Year to Date Return, Label

rr_YearToDateReturnLabel

Year-to-Date Return

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Sep. 30, 2014

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

4.58%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Highest Quarter Return

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Sep. 30, 2009

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

19.83%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Lowest Quarter Return

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Dec. 31, 2008

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(25.37%)

A T B C | Fidelity Advisor Value Leaders Fund | Class T

Risk/Return:

rr_RiskReturnAbstract

Maximum sales charge (load) on purchases (as a % of offering price)

rr_MaximumCumulativeSalesChargeOverOfferingPrice

3.50%

Maximum contingent deferred sales charge (as a % of the lesser of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

^[1]

Management fee (fluctuates based on the fund's performance relative to a securities market index)

rr_ManagementFeesOverAssets

0.36%

Distribution and/or Service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

0.50%

Other expenses

rr_OtherExpensesOverAssets

0.72%

Acquired fund fees and expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.08%

Total annual operating expenses

rr_ExpensesOverAssets

1.66%

^[2]

Expenses Deferred Charges [Text Block]

rr_ExpensesDeferredChargesTextBlock

Class A and Class T purchases of $1 million or more will not be subject to a front-end sales charge. Such Class A and Class T purchases may be subject, upon redemption, to a contingent deferred sales charge (CDSC) of 1.00% or 0.25%, respectively.

1 year

rr_ExpenseExampleYear01

513

3 years

rr_ExpenseExampleYear03

855

5 years

rr_ExpenseExampleYear05

1,221

10 years

rr_ExpenseExampleYear10

2,247

1 year

rr_ExpenseExampleNoRedemptionYear01

513

3 years

rr_ExpenseExampleNoRedemptionYear03

855

5 years

rr_ExpenseExampleNoRedemptionYear05

1,221

10 years

rr_ExpenseExampleNoRedemptionYear10

2,247

A T B C | Fidelity Advisor Value Leaders Fund | Class B

Risk/Return:

rr_RiskReturnAbstract

Maximum sales charge (load) on purchases (as a % of offering price)

rr_MaximumCumulativeSalesChargeOverOfferingPrice

none

Maximum contingent deferred sales charge (as a % of the lesser of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

5.00%

^[3]

Management fee (fluctuates based on the fund's performance relative to a securities market index)

rr_ManagementFeesOverAssets

0.36%

Distribution and/or Service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

1.00%

Other expenses

rr_OtherExpensesOverAssets

0.76%

Acquired fund fees and expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.08%

Total annual operating expenses

rr_ExpensesOverAssets

2.20%

^[2]

Expenses Deferred Charges [Text Block]

rr_ExpensesDeferredChargesTextBlock

Declines over 6 years from 5.00% to 0%.

1 year

rr_ExpenseExampleYear01

723

3 years

rr_ExpenseExampleYear03

988

5 years

rr_ExpenseExampleYear05

1,380

10 years

rr_ExpenseExampleYear10

2,229

1 year

rr_ExpenseExampleNoRedemptionYear01

223

3 years

rr_ExpenseExampleNoRedemptionYear03

688

5 years

rr_ExpenseExampleNoRedemptionYear05

1,180

10 years

rr_ExpenseExampleNoRedemptionYear10

2,229

A T B C | Fidelity Advisor Value Leaders Fund | Class C

Risk/Return:

rr_RiskReturnAbstract

Maximum sales charge (load) on purchases (as a % of offering price)

rr_MaximumCumulativeSalesChargeOverOfferingPrice

none

Maximum contingent deferred sales charge (as a % of the lesser of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

1.00%

^[4]

Management fee (fluctuates based on the fund's performance relative to a securities market index)

rr_ManagementFeesOverAssets

0.36%

Distribution and/or Service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

1.00%

Other expenses

rr_OtherExpensesOverAssets

0.73%

Acquired fund fees and expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.08%

Total annual operating expenses

rr_ExpensesOverAssets

2.17%

^[2]

Expenses Deferred Charges [Text Block]

rr_ExpensesDeferredChargesTextBlock

On Class C shares redeemed less than one year after purchase.

1 year

rr_ExpenseExampleYear01

320

3 years

rr_ExpenseExampleYear03

679

5 years

rr_ExpenseExampleYear05

1,164

10 years

rr_ExpenseExampleYear10

2,503

1 year

rr_ExpenseExampleNoRedemptionYear01

220

3 years

rr_ExpenseExampleNoRedemptionYear03

679

5 years

rr_ExpenseExampleNoRedemptionYear05

1,164

10 years

rr_ExpenseExampleNoRedemptionYear10

2,503

A T B C | Fidelity Advisor Value Leaders Fund | Return Before Taxes | Class A

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Class A - Return Before Taxes

Past 1 year

rr_AverageAnnualReturnYear01

26.85%

Past 5 years

rr_AverageAnnualReturnYear05

13.11%

Past 10 years

rr_AverageAnnualReturnYear10

4.29%

A T B C | Fidelity Advisor Value Leaders Fund | Return Before Taxes | Class T

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Class T - Return Before Taxes

Past 1 year

rr_AverageAnnualReturnYear01

29.58%

Past 5 years

rr_AverageAnnualReturnYear05

13.37%

Past 10 years

rr_AverageAnnualReturnYear10

4.28%

A T B C | Fidelity Advisor Value Leaders Fund | Return Before Taxes | Class B

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Class B - Return Before Taxes

Past 1 year

rr_AverageAnnualReturnYear01

28.70%

Past 5 years

rr_AverageAnnualReturnYear05

13.37%

Past 10 years

rr_AverageAnnualReturnYear10

4.36%

A T B C | Fidelity Advisor Value Leaders Fund | Return Before Taxes | Class C

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Class C - Return Before Taxes

Past 1 year

rr_AverageAnnualReturnYear01

32.61%

Past 5 years

rr_AverageAnnualReturnYear05

13.61%

Past 10 years

rr_AverageAnnualReturnYear10

4.12%

A T B C | Fidelity Advisor Value Leaders Fund | Return After Taxes on Distributions | Class A

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Class A - Return After Taxes on Distributions

Past 1 year

rr_AverageAnnualReturnYear01

26.85%

Past 5 years

rr_AverageAnnualReturnYear05

12.93%

Past 10 years

rr_AverageAnnualReturnYear10

3.95%

A T B C | Fidelity Advisor Value Leaders Fund | Return After Taxes on Distributions and Sale of Fund Shares | Class A

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Class A - Return After Taxes on Distributions and Sale of Fund Shares

Past 1 year

rr_AverageAnnualReturnYear01

15.20%

Past 5 years

rr_AverageAnnualReturnYear05

10.55%

Past 10 years

rr_AverageAnnualReturnYear10

3.50%

A T B C | Fidelity Advisor Value Leaders Fund | Russell 1000® Value Index (reflects no deduction for fees, expenses, or taxes)

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Russell 1000^® Value Index

Past 1 year

rr_AverageAnnualReturnYear01

32.53%

Past 5 years

rr_AverageAnnualReturnYear05

16.67%

Past 10 years

rr_AverageAnnualReturnYear10

7.58%

[1] Class A and Class T purchases of $1 million or more will not be subject to a front-end sales charge. Such Class A and Class T purchases may be subject, upon redemption, to a contingent deferred sales charge (CDSC) of 1.00% or 0.25%, respectively.

[2] Differs from the ratios of expenses to average net assets in the Financial Highlights section of the prospectus because of acquired fund fees and expenses.

[3] Declines over 6 years from 5.00% to 0%.

[4] On Class C shares redeemed less than one year after purchase.