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Risk/Return: rr_RiskReturnAbstract  
Registrant Name dei_EntityRegistrantName FIDELITY ADVISOR SERIES I
Prospectus Date rr_ProspectusDate Jun. 04, 2012
Fidelity Stock Selector Mid Cap Fund | Fidelity Advisor Stock Selector Mid Cap Fund
  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading Fund Summary

Fund/Class:
Fidelity Advisor® Stock Selector Mid Cap Fund/Fidelity® Stock Selector Mid Cap Fund
Objective [Heading] rr_ObjectiveHeading Investment Objective
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock The fund seeks long-term growth of capital.
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, hold, or sell shares of the fund.
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption Shareholder fees
(fees paid directly from your investment)
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual class 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 198% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 198.00%
Other Expenses, New Fund, Based on Estimates [Text] rr_OtherExpensesNewFundBasedOnEstimates Based on estimated amounts for the current fiscal year.
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 mutual 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:
Strategy [Heading] rr_StrategyHeading Principal Investment Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock
  • Normally investing at least 80% of assets in stocks of companies with medium market capitalizations (which, for purposes of this fund, are those companies with market capitalizations similar to companies in the Russell Midcap® Index or the S&P MidCap 400® Index).
  • Potentially investing in companies with smaller or larger market capitalizations.
  • Investing in domestic and foreign issuers.
  • Allocating the fund's assets across different market sectors (at present, consumer discretionary, consumer staples, energy, financials, health care, industrials, information technology, materials, telecom services, and utilities), using different Fidelity managers.
  • Investing in either "growth" stocks or "value" stocks or both.
  • 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 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. The value of securities of smaller issuers can be more volatile than that of larger issuers.
  • Mid Cap Investing. The value of securities of medium size, less well-known issuers can perform differently from the market as a whole and other types of stocks and can be more volatile than that of larger issuers.

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] rr_BarChartAndPerformanceTableHeading 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 Information about the Index 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 history will be available for the class of shares offered through this prospectus after the class has been in operation for one calendar year.
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] rr_BarChartHeading Year-by-Year Returns
Calendar Years		 [1]
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock

During the periods shown in the chart for Institutional Class:

Returns

Quarter ended

Highest Quarter Return

24.14%

June 30, 2009

Lowest Quarter Return

-30.10%

December 31, 2008

Year-to-Date Return

15.28%

March 31, 2012
Bar Chart, Returns for Class Not Offered in Prospectus [Text] rr_BarChartReturnsForClassNotOfferedInProspectus The returns shown above are for Institutional Class, which is not offered through this prospectus. Fidelity Stock Selector Mid Cap Fund would have substantially similar annual returns to Institutional Class because the classes are invested in the same portfolio of securities. Fidelity Stock Selector Mid Cap Fund's returns would differ from Institutional Class's returns to the extent that the classes do not have the same expenses.
Performance Table Heading rr_PerformanceTableHeading Average Annual Returns
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 Institutional Class are shown in the table below and after-tax returns for other classes will vary.
Performance Table Explanation after Tax Higher rr_PerformanceTableExplanationAfterTaxHigher Return After Taxes on Distributions and Sale of Fund Shares may be higher than other returns for the same period due to a tax benefit of realizing a capital loss upon the sale of fund shares.
Performance Table Narrative rr_PerformanceTableNarrativeTextBlock 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 Institutional Class 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. Return After Taxes on Distributions and Sale of Fund Shares may be higher than other returns for the same period due to a tax benefit of realizing a capital loss upon the sale of fund shares.

For the periods ended
December 31, 2011
Fidelity Stock Selector Mid Cap Fund | Fidelity Advisor Stock Selector Mid Cap Fund | Class: Fidelity Stock Selector Mid Cap Fund
  
Risk/Return: rr_RiskReturnAbstract  
Shareholder fees (fees paid directly from your investment) rr_ShareholderFeeOther none
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 none
Other Expenses rr_OtherExpensesOverAssets 0.31% [2]
Acquired fund fees and expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.02% [2]
Total annual operating expenses rr_ExpensesOverAssets 0.69%
1 year rr_ExpenseExampleYear01 70
3 years rr_ExpenseExampleYear03 221
5 years rr_ExpenseExampleYear05 384
10 years rr_ExpenseExampleYear10 859
Performance One Year or Less [Text] rr_PerformanceOneYearOrLess Performance history will be available for the class of shares offered through this prospectus after the class has been in operation for one calendar year.
Fidelity Stock Selector Mid Cap Fund | Fidelity Advisor Stock Selector Mid Cap Fund | Institutional Class
  
Risk/Return: rr_RiskReturnAbstract  
2002 rr_AnnualReturn2002 (18.16%) [1]
2003 rr_AnnualReturn2003 44.56% [1]
2004 rr_AnnualReturn2004 16.45% [1]
2005 rr_AnnualReturn2005 8.79% [1]
2006 rr_AnnualReturn2006 13.59% [1]
2007 rr_AnnualReturn2007 10.03% [1]
2008 rr_AnnualReturn2008 (52.19%) [1]
2009 rr_AnnualReturn2009 47.24% [1]
2010 rr_AnnualReturn2010 24.37% [1]
2011 rr_AnnualReturn2011 (4.77%) [1]
Year to Date Return, Label rr_YearToDateReturnLabel Year-to-Date Return
Bar Chart, Year to Date Return, Date rr_BarChartYearToDateReturnDate Mar. 31, 2012
Bar Chart, Year to Date Return rr_BarChartYearToDateReturn 15.28%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarter Return
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2009
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 24.14%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarter Return
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2008
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (30.10%)
Fidelity Stock Selector Mid Cap Fund | Fidelity Advisor Stock Selector Mid Cap Fund | Return Before Taxes | Institutional Class
  
Risk/Return: rr_RiskReturnAbstract  
Column rr_AverageAnnualReturnColumnName Institutional Class
Label rr_AverageAnnualReturnLabel Return Before Taxes
Past 1 year rr_AverageAnnualReturnYear01 (4.77%) [1]
Past 5 years rr_AverageAnnualReturnYear05 (1.71%) [1]
Past 10 years rr_AverageAnnualReturnYear10 4.56% [1]
Fidelity Stock Selector Mid Cap Fund | Fidelity Advisor Stock Selector Mid Cap Fund | Return After Taxes on Distributions | Institutional Class
  
Risk/Return: rr_RiskReturnAbstract  
Column rr_AverageAnnualReturnColumnName Institutional Class
Label rr_AverageAnnualReturnLabel Return After Taxes on Distributions
Past 1 year rr_AverageAnnualReturnYear01 (4.90%) [1]
Past 5 years rr_AverageAnnualReturnYear05 (2.36%) [1]
Past 10 years rr_AverageAnnualReturnYear10 3.76% [1]
Fidelity Stock Selector Mid Cap Fund | Fidelity Advisor Stock Selector Mid Cap Fund | Return After Taxes on Distributions and Sale of Fund Shares | Institutional Class
  
Risk/Return: rr_RiskReturnAbstract  
Column rr_AverageAnnualReturnColumnName Institutional Class
Label rr_AverageAnnualReturnLabel Return After Taxes on Distributions and Sale of Fund Shares
Past 1 year rr_AverageAnnualReturnYear01 (2.94%) [1]
Past 5 years rr_AverageAnnualReturnYear05 (1.56%) [1]
Past 10 years rr_AverageAnnualReturnYear10 3.84% [1]
Fidelity Stock Selector Mid Cap Fund | Fidelity Advisor Stock Selector Mid Cap Fund | S&P MidCap 400 Index (reflects no deduction for fees, expenses, or taxes)
  
Risk/Return: rr_RiskReturnAbstract  
Label rr_AverageAnnualReturnLabel S&P MidCap 400® Index
Past 1 year rr_AverageAnnualReturnYear01 (1.73%) [1]
Past 5 years rr_AverageAnnualReturnYear05 3.32% [1]
Past 10 years rr_AverageAnnualReturnYear10 7.04% [1]
[1] The returns shown above are for Institutional Class, which is not offered through this prospectus. Fidelity Stock Selector Mid Cap Fund would have substantially similar annual returns to Institutional Class because the classes are invested in the same portfolio of securities. Fidelity Stock Selector Mid Cap Fund's returns would differ from Institutional Class's returns to the extent that the classes do not have the same expenses.
[2] Based on estimated amounts for the current fiscal year.