Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	FIDELITY SECURITIES FUND
Prospectus Date	rr_ProspectusDate	Sep. 29, 2014
Series | Fidelity Series Blue Chip Growth Fund
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	Fund Summary Fund/Class: Fidelity® Series Blue Chip Growth Fund /Fidelity Series Blue Chip Growth Fund
Objective [Heading]	rr_ObjectiveHeading	Investment Objective
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	The fund seeks growth of capital over the long term.
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.
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. For the period from November 7, 2013 to July 31, 2014, the fund's portfolio turnover rate was 67% (annualized) of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	67.00%
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:
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 companies that Fidelity Management & Research Company (FMR) believes have above-average growth potential (stocks of these companies are often called "growth" 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.
Strategy Portfolio Concentration [Text]	rr_StrategyPortfolioConcentration	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).
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. "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	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 One Year or Less [Text]	rr_PerformanceOneYearOrLess	Performance history will be available for the fund after the fund has been in operation for one calendar year.
Series | Fidelity Series Blue Chip Growth Fund | Class: Fidelity Series Blue Chip Growth 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	0.55%
Distribution and/or Service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	none
Other expenses	rr_OtherExpensesOverAssets	0.19%
Total annual operating expenses	rr_ExpensesOverAssets	0.74%
1 year	rr_ExpenseExampleYear01	76
3 years	rr_ExpenseExampleYear03	237
5 years	rr_ExpenseExampleYear05	411
10 years	rr_ExpenseExampleYear10	$ 918