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Class T Prospectus | DREYFUS THIRD CENTURY FUND INC  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading Fund Summary
Objective [Heading] rr_ObjectiveHeading Investment Objective
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock

The fund seeks to provide capital growth,
Objective, Secondary [Text Block] rr_ObjectiveSecondaryTextBlock

with current income as a secondary goal.
Expense [Heading] rr_ExpenseHeading Fees and Expenses
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold shares of the fund. You may qualify for sales charge discounts if you invest at least $250,000 in the fund. More information about sales charges, including such discounts, is available from your financial professional and in the Shareholder Guide section beginning on page 9 of the prospectus and in the How to Buy Shares section and the Additional Information About How to Buy Shares section beginning on page II-1 and page III-1, respectively, of the fund's Statement of Additional Information.
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual Fund Operating Expenses (expenses that you pay each year as a percentage 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 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 fund operating expenses or in the Example, affect the fund's performance. During the most recent fiscal year, the fund's portfolio turnover rate was 61.45% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 61.45%
Expense Breakpoint Discounts [Text] rr_ExpenseBreakpointDiscounts You may qualify for sales charge discounts if you invest at least $250,000 in the fund.
Expense Breakpoint, Minimum Investment Required [Amount] rr_ExpenseBreakpointMinimumInvestmentRequiredAmount $ 250,000
Expense Example [Heading] rr_ExpenseExampleHeading Example
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock

The Example is intended to help you compare the cost of investing in the fund with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the fund for the time periods indicated and then hold or redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the fund's operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Strategy [Heading] rr_StrategyHeading Principal Investment Strategy
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock

To pursue its goals, the fund, under normal circumstances, invests at least 80% of its net assets in the common stocks of companies that, in the opinion of the fund's management, meet traditional investment standards and conduct their business in a manner that contributes to the enhancement of the quality of life in America.


The fund's investment strategy combines a disciplined investment process that consists of computer modeling techniques, fundamental analysis and risk management with a social investment process. In selecting stocks, the portfolio managers begin by using computer models to identify and rank stocks within an industry or sector, based on several characteristics, including value, growth and financial profile.


Next, based on fundamental analysis, the portfolio managers designate the most attractive of the higher ranked securities as potential purchase candidates, drawing on a variety of sources, including company management and internal as well as Wall Street research.


The portfolio managers then evaluate each stock considered to be a potential purchase candidate, by industry or sector, to determine whether the company enhances the quality of life in America by considering its record in the areas of protection and improvement of the environment and the proper use of our natural resources, occupational health and safety, consumer protection and product purity and equal employment opportunity.


The portfolio managers then further examine the companies determined to be eligible for purchase, by industry or sector, and select investments from those companies the portfolio managers consider to be the most attractive based on financial considerations.


The fund normally focuses on large-cap growth stocks but also may invest in value-oriented stocks, mid-cap stocks and small-cap stocks.
Risk [Heading] rr_RiskHeading Principal Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock

An investment in the fund is not a bank deposit. It is not insured or guaranteed by the Federal Deposit Insurance Corporation (FDIC) or any other government agency. It is not a complete investment program. The fund's share price fluctuates, sometimes dramatically, which means you could lose money.


· Risks of stock investing. Stocks generally fluctuate more in value than bonds and may decline significantly over short time periods. There is the chance that stock prices overall will decline because stock markets tend to move in cycles, with periods of rising prices and falling prices. The market value of a stock may decline due to general market conditions or because of factors that affect the particular company or the company's industry.


· Social investment risk. Socially responsible investment criteria may limit the number of investment opportunities available to the fund, and as a result, at times the fund's returns may be lower than those funds that are not subject to such special investment considerations. If the portfolio managers determine that a company in the fund's portfolio fails to meet the fund's social criteria, the company's stock will be sold as soon as reasonably possible, consistent with the best interests of the fund.


· Large cap stock risk. To the extent the fund invests in large capitalization stocks, the fund may underperform funds that invest primarily in the stocks of lower quality, smaller capitalization companies during periods when the stocks of such companies are in favor.


· Small and midsize company risk. Small and midsize companies carry additional risks because the operating histories of these companies tend to be more limited, their earnings and revenues less predictable (and some companies may be experiencing significant losses), and their share prices more volatile than those of larger, more established companies. These companies may have limited product lines, markets or financial resources, or may depend on a limited management group. Other investments are made in anticipation of future products, services or events whose delay or cancellation could cause the stock price to drop. The shares of smaller companies tend to trade less frequently than those of larger, more established companies, which can adversely affect the pricing of these securities and the fund's ability to sell these securities. Some of the fund's investments will rise and fall based on investor perception rather than economic factors.


· Growth stock risk. Investors often expect growth companies to increase their earnings at a certain rate. If these expectations are not met, investors can punish the stocks inordinately, even if earnings do increase. In addition, growth stocks may lack the dividend yield that may cushion stock prices in market downturns.


· Value stock risk. Value stocks involve the risk that they may never reach their expected full market value, either because the market fails to recognize the stock's intrinsic worth or the expected value was misgauged. They also may decline in price even though in theory they are already undervalued.
Risk Lose Money [Text] rr_RiskLoseMoney The fund's share price fluctuates, sometimes dramatically, which means you could lose money.
Risk Not Insured Depository Institution [Text] rr_RiskNotInsuredDepositoryInstitution An investment in the fund is not a bank deposit. It is not insured or guaranteed by the Federal Deposit Insurance Corporation (FDIC) or any other government agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Performance
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock

The following bar chart and table provide some indication of the risks of investing in the fund. The bar chart shows changes in the performance of the fund's Class T shares from year to year. Sales charges are not reflected in the bar chart, and, if those charges were included, returns would have been less than those shown. The table compares the average annual total returns of the fund's Class T shares to those of a broad measure of market performance. The fund's past performance (before and after taxes) is not necessarily an indication of how the fund will perform in the future. More recent performance information may be available at www.dreyfus.com.


The historical performance of the fund's Class A shares, which are not offered in this prospectus, is used to calculate the performance of the fund's Class T shares shown in the bar chart and table. Since the fund's Class T shares are new, past performance information is not available for Class T shares as of the date of this prospectus. Each share class is invested in the same portfolio of securities, and the annual returns would have differed only to the extent that the classes do not have the same charges and expenses. The performance figures in the table have been adjusted to reflect the sales load applicable to the fund's Class T shares. The performance figures have not been adjusted to reflect applicable class fees and expenses.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The following bar chart and table provide some indication of the risks of investing in the fund.
Performance One Year or Less [Text] rr_PerformanceOneYearOrLess Since the fund's Class T shares are new, past performance information is not available for Class T shares as of the date of this prospectus.
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress www.dreyfus.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture The fund's past performance (before and after taxes) is not necessarily an indication of how the fund will perform in the future.
Bar Chart [Heading] rr_BarChartHeading Year-by-Year Total Returns as of 12/31 each year (%) Class T*
Bar Chart Does Not Reflect Sales Loads [Text] rr_BarChartDoesNotReflectSalesLoads Sales charges are not reflected in the bar chart, and, if those charges were included, returns would have been less than those shown.
Bar Chart Footnotes [Text Block] rr_BarChartFootnotesTextBlock

* Reflects the performance of the fund's Class A shares, which are offered in a separate prospectus. Such performance figures have not been adjusted to reflect applicable class fees and expenses.
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock
   
 

Best Quarter
Q2, 2009: 17.11%

Worst Quarter
Q4, 2008: -21.37%
Bar Chart, Returns for Class Not Offered in Prospectus [Text] rr_BarChartReturnsForClassNotOfferedInProspectus The historical performance of the fund's Class A shares, which are not offered in this prospectus, is used to calculate the performance of the fund's Class T shares shown in the bar chart and table.
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Best Quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2009
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 17.11%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Worst Quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2008
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (21.37%)
Performance Table Does Reflect Sales Loads rr_PerformanceTableDoesReflectSalesLoads The performance figures in the table have been adjusted to reflect the sales load applicable to the fund's Class T shares.
Index No Deduction for Fees, Expenses, Taxes [Text] rr_IndexNoDeductionForFeesExpensesTaxes reflects no deduction for fees, expenses, or taxes
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate After-tax returns are calculated using the historical highest individual federal marginal income tax rates, and do not reflect the impact of state and local taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred Actual after-tax returns depend on the investor's tax situation and may differ from those shown, and the after-tax returns shown are not relevant to investors who hold their shares through U.S. tax-deferred arrangements such as 401(k) plans or individual retirement accounts.
Performance Table Narrative rr_PerformanceTableNarrativeTextBlock

After-tax returns are calculated using the historical highest individual federal marginal income tax rates, and do not reflect the impact of state and local taxes. Actual after-tax returns depend on the investor's tax situation and may differ from those shown, and the after-tax returns shown are not relevant to investors who hold their shares through U.S. tax-deferred arrangements such as 401(k) plans or individual retirement accounts.
Caption rr_AverageAnnualReturnCaption Average Annual Total Returns (as of 12/31/16)
Class T Prospectus | DREYFUS THIRD CENTURY FUND INC | S&P 500® Index reflects no deduction for fees, expenses or taxes  
Risk/Return: rr_RiskReturnAbstract  
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 11.94%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 14.65%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 6.94%
Class T Prospectus | DREYFUS THIRD CENTURY FUND INC | Class T  
Risk/Return: rr_RiskReturnAbstract  
Maximum sales charge (load) imposed on purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 2.50%
Maximum deferred sales charge (load) (as a percentage of lower of purchase or sale price) rr_MaximumDeferredSalesChargeOverOther none
Management fees rr_ManagementFeesOverAssets 0.75%
Distribution/service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses rr_OtherExpensesOverAssets 0.24%
Total annual fund operating expenses rr_ExpensesOverAssets 1.24%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 373
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 634
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 914
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,712
Class T Prospectus | DREYFUS THIRD CENTURY FUND INC | Class A  
Risk/Return: rr_RiskReturnAbstract  
Annual Return 2007 rr_AnnualReturn2007 7.34%
Annual Return 2008 rr_AnnualReturn2008 (34.55%)
Annual Return 2009 rr_AnnualReturn2009 33.03%
Annual Return 2010 rr_AnnualReturn2010 14.28%
Annual Return 2011 rr_AnnualReturn2011 0.37%
Annual Return 2012 rr_AnnualReturn2012 11.34%
Annual Return 2013 rr_AnnualReturn2013 33.76%
Annual Return 2014 rr_AnnualReturn2014 12.93%
Annual Return 2015 rr_AnnualReturn2015 (3.38%)
Annual Return 2016 rr_AnnualReturn2016 9.86%
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 7.12% [1]
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 11.73% [1]
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 6.43% [1]
Class T Prospectus | DREYFUS THIRD CENTURY FUND INC | Class A | After Taxes on Distributions  
Risk/Return: rr_RiskReturnAbstract  
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 5.82% [1]
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 9.91% [1]
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 5.54% [1]
Class T Prospectus | DREYFUS THIRD CENTURY FUND INC | Class A | After Taxes on Distributions and Sale of Fund Shares  
Risk/Return: rr_RiskReturnAbstract  
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 5.06% [1]
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 9.24% [1]
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 5.13% [1]
[1] Reflects the performance of the fund's Class A shares, which are offered in a separate prospectus, adjusted to reflect applicable sales charges. Such performance figures have not been adjusted to reflect applicable class fees and expenses.