XML 25 R57.htm IDEA: XBRL DOCUMENT v3.19.3.a.u2
Label Element Value
Risk/Return: rr_RiskReturnAbstract  
Registrant Name dei_EntityRegistrantName FIDELITY MT VERNON STREET TRUST
Prospectus Date rr_ProspectusDate Jan. 29, 2020
11.30 Fidelity Growth Strategies K6 Fund PRO-05 | Fidelity Growth Strategies K6 Fund  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading <p style="font: bold 20pt Arial, Helvetica, sans-serif;">Fund Summary</p><p style="font: bold 12pt Arial, Helvetica, sans-serif;">Fund:<br/>Fidelity® Growth Strategies K6 Fund</p>
Objective [Heading] rr_ObjectiveHeading <font style="font: bold 16pt Arial, Helvetica, sans-serif;">Investment Objective</font>
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock

The fund seeks capital appreciation.
Expense [Heading] rr_ExpenseHeading <font style="font: bold 16pt Arial, Helvetica, sans-serif;"><b>Fee Table</b></font>
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.

Shareholder Fees Caption [Text] rr_ShareholderFeesCaption <p style="font: bold 11pt Arial, sans-serif; margin-bottom: 0px;">Shareholder fees</p><p style="font: bold 9pt Arial, sans-serif; margin-top: 0px"></p>
(fees paid directly from your investment) rr_ShareholderFeeOther none
Operating Expenses Caption [Text] rr_OperatingExpensesCaption <p style="font: bold 11pt Arial, sans-serif; margin-bottom: 0px;">Annual Operating Expenses</p><p style="font: bold 9pt Arial, sans-serif; margin-top: 0px">(expenses that you pay each year as a % of the value of your investment)</p>
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading <font style="font: bold 16pt Arial, Helvetica, sans-serif;"><b>Portfolio Turnover</b></font>
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 66% of the average value of its portfolio.

Portfolio Turnover, Rate rr_PortfolioTurnoverRate 66.00%
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:

Expense Example by, Year, Caption [Text] rr_ExpenseExampleByYearCaption <p style="font: bold 9pt Arial, sans-serif; margin-top: 0px">Sell All Shares</p>
Strategy [Heading] rr_StrategyHeading <font style="font: bold 16pt Arial, Helvetica, sans-serif;"><b>Principal Investment Strategies</b></font>
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock
  • Normally investing primarily in common stocks.
  • Normally investing in companies that Fidelity Management & Research Company LLC (FMR) believes offer the potential for accelerated earnings or revenue growth (stocks of these companies are often called "growth" stocks).
  • Focusing investments in medium-sized companies, but may also invest substantially in larger or smaller companies.
  • Investing in 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 <font style="font: bold 16pt Arial, Helvetica, sans-serif;"><b>Principal Investment Risks</b></font>
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. The value of securities of smaller issuers can be more volatile than that of larger issuers.
  • "Growth" Investing. "Growth" stocks can perform differently from the market as a whole and other types of stocks and can be more volatile than other types of stocks.

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 <font style="FONT-FAMILY: Times New Roman" size="3">You could lose money by investing in the fund.</font>
Risk Not Insured Depository Institution [Text] rr_RiskNotInsuredDepositoryInstitution <font style="FONT-FAMILY: Times New Roman" size="3">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.</font>
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading <font style="font: bold 16pt Arial, Helvetica, sans-serif;"><b>Performance</b></font>
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.401k.com and log in or www.fidelity.com for more recent performance information.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns <font style="FONT-FAMILY: Times New Roman" size="3">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.</font>
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress <font style="FONT-FAMILY: Times New Roman" size="3">www.401k.com and log in or www.fidelity.com </font>
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture <font style="FONT-FAMILY: Times New Roman" size="3">Past performance (before and after taxes) is not an indication of future performance.</font>
Bar Chart [Heading] rr_BarChartHeading <p style="font:bold 11pt Arial, sans-serif; margin-bottom: 0px;">Year-by-Year Returns</p><p style="font: bold 9pt Arial, sans-serif; margin-top: 0px">Calendar Years</p>
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock
During the periods shown in the chart:ReturnsQuarter ended
Highest Quarter Return16.54%March 31, 2019
Lowest Quarter Return-14.53%December 31, 2018
Performance Table Heading rr_PerformanceTableHeading <font style="font: bold 16pt Arial, Helvetica, sans-serif;"><b>Average Annual Returns</b></font>
Performance Table Narrative rr_PerformanceTableNarrativeTextBlock

For the periods ended December 31, 2019
11.30 Fidelity Growth Strategies K6 Fund PRO-05 | Fidelity Growth Strategies K6 Fund | Fidelity Growth Strategies K6 Fund  
Risk/Return: rr_RiskReturnAbstract  
Management fee rr_ManagementFeesOverAssets 0.45%
Distribution and/or Service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets none
Total annual operating expenses rr_ExpensesOverAssets 0.45%
1 year rr_ExpenseExampleYear01 $ 46
3 years rr_ExpenseExampleYear03 144
5 years rr_ExpenseExampleYear05 252
10 years rr_ExpenseExampleYear10 $ 567
2018 rr_AnnualReturn2018 (6.92%)
2019 rr_AnnualReturn2019 36.90%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarter Return
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Mar. 31, 2019
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 16.54%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarter Return
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2018
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (14.53%)
Inception Date rr_AverageAnnualReturnInceptionDate May 25, 2017
11.30 Fidelity Growth Strategies K6 Fund PRO-05 | Fidelity Growth Strategies K6 Fund | Return Before Taxes | Fidelity Growth Strategies K6 Fund  
Risk/Return: rr_RiskReturnAbstract  
Column rr_AverageAnnualReturnColumnName Fidelity Growth Strategies K6 Fund
Label rr_AverageAnnualReturnLabel <font style="FONT-FAMILY: Times New Roman" ><b>Fidelity® Growth Strategies K6 Fund</b></font>
Past 1 year rr_AverageAnnualReturnYear01 36.90%
Since Inception rr_AverageAnnualReturnSinceInception 14.02% [1]
11.30 Fidelity Growth Strategies K6 Fund PRO-05 | Fidelity Growth Strategies K6 Fund | Russell Midcap® Growth Index(reflects no deduction for fees, expenses, or taxes)  
Risk/Return: rr_RiskReturnAbstract  
Past 1 year rr_AverageAnnualReturnYear01 35.47%
Since Inception rr_AverageAnnualReturnSinceInception 15.51% [1]
[1] From May 25, 2017