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T. Rowe Price New Horizons Fund, Inc.  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading New Horizons Fund
Objective [Heading] rr_ObjectiveHeading Investment Objective(s)
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock

The fund seeks long-term capital growth by investing primarily in common stocks of small, rapidly growing companies.
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, hold, and sell shares of the fund. You may also incur brokerage commissions and other charges when buying or selling shares of the Investor Class or I Class, which are not reflected in the table.
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 rate may indicate higher transaction costs and may result in higher taxes when the fund’s 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 52.2% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 52.20%
Expense Example [Heading] rr_ExpenseExampleHeading Example
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock This 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 redeem all of your shares at the end of those periods, that your investment has a 5% return each year, and that the fund’s operating expenses remain the same. The example also assumes that any current expense limitation arrangement remains in place for the period noted in the table above; therefore, the figures have been adjusted to reflect fee waivers or expense reimbursements only in the periods for which the expense limitation arrangement is expected to continue. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Strategy [Heading] rr_StrategyHeading Principal Investment Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock

The fund invests primarily in a diversified group of small, emerging growth companies, preferably early in their corporate life cycle before the companies become widely recognized by the investment community. The fund may also invest in companies that offer the possibility of accelerating earnings growth because of rejuvenated management, new products, or structural changes in the economy. The portfolio manager will not necessarily sell a position in a company that has grown beyond the developing stage if the company still fits the fund’s other investment criteria.

When choosing stocks for the fund’s portfolio, T. Rowe Price analysts tend to look for small growth companies that exhibit some or all of the following characteristics:

·   effective management;

·   operate in fertile growth areas;

·   demonstrate innovative research, product development, and marketing;

·   provide efficient service;

·   possess pricing flexibility; and

·   employ sound financial and accounting policies.

While most assets will typically be invested in U.S. common stocks, the fund may invest in foreign stocks in keeping with its objective(s).The fund’s investments may include holdings in privately held companies and companies that only recently began to trade publicly.

Risk [Heading] rr_RiskHeading Principal Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock

As with any fund, there is no guarantee that the fund will achieve its objective(s). The fund’s share price fluctuates, which means you could lose money by investing in the fund. The principal risks of investing in this fund, which may be even greater during periods of market disruption or volatility, are summarized as follows:

 

Small-cap stocks Investments in securities issued by small-cap companies are likely to be more volatile than investments in securities issued by larger companies. Small-cap companies often have less experienced management, narrower product lines, more limited financial resources, and less publicly available information than larger companies. In addition, smaller

companies are typically more sensitive to changes in overall economic conditions and their securities may be difficult to trade.

Private placements and IPOs Investments in the stocks of privately held companies and in companies that only recently began to publicly trade, such as initial public offerings or IPOs, involve greater risks than investments in stocks of companies that have traded publicly on an exchange for extended time periods. There is significantly less information available about these companies’ business models, quality of management, earnings growth potential, and other criteria that are normally considered when evaluating the investment prospects of a company. Private placements and other restricted securities held by the fund are typically considered to be illiquid and tend to be difficult to value since there are no market prices and less overall financial information available. The adviser evaluates a variety of factors when assigning a value to these holdings, but the determination involves some degree of subjectivity and the value assigned for the fund may differ from the value assigned by other mutual funds holding the same security.

Growth investing The fund’s growth approach to investing could cause it to underperform other stock funds that employ a different investment style. Growth stocks tend to be more volatile than certain other types of stocks, and their prices may fluctuate more dramatically than the overall stock market. A stock with growth characteristics can have sharp price declines due to decreases in current or expected earnings and may lack dividends that can help cushion its share price in a declining market.

Market conditions The value of the fund’s investments may decrease, sometimes rapidly or unexpectedly, due to factors affecting an issuer held by the fund, particular industries, or the overall securities markets. A variety of factors can increase the volatility of the fund’s holdings and markets generally, including political or regulatory developments, recessions, inflation, rapid interest rate changes, war or acts of terrorism, natural disasters, and outbreaks of infectious illnesses or other widespread public health issues such as the coronavirus pandemic and related governmental and public responses. Certain events may cause instability across global markets, including reduced liquidity and disruptions in trading markets, while some events may affect certain geographic regions, countries, sectors, and industries more significantly than others. Government intervention in markets may impact interest rates, market volatility, and security pricing. These adverse developments may cause broad declines in market value due to short-term market movements or for significantly longer periods during more prolonged market downturns.

Sector exposure At times, the fund may have a significant portion of its assets invested in securities of issuers conducting business in a broadly related group of industries within the same economic sector. Issuers in the same economic sector may be similarly affected by economic or market events, making the fund more vulnerable to unfavorable developments in that economic sector than funds that invest more broadly. Investments in the technology sector are susceptible to intense competition, government regulation, changing consumer preferences, and dependency on patent protection.

Foreign investing Investments in the securities of non-U.S. issuers may be adversely affected by local, political, social, and economic conditions overseas, greater volatility, reduced liquidity, or decreases in foreign currency values relative to the U.S. dollar. The risks of investing outside the U.S. are heightened for any investments in emerging markets, which are susceptible to greater volatility than investments in developed markets.

Stock investing Stocks generally fluctuate in value more than bonds and may decline significantly over short time periods. There is a chance that stock prices overall will decline because stock markets tend to move in cycles, with periods of rising and falling prices. The value of stocks held by the fund may decline due to general weakness or volatility in the stock markets in which the fund invests or because of factors that affect a particular company or industry.

Liquidity A particular investment or an entire market segment may become less liquid or even illiquid, sometimes abruptly, which could limit the fund’s ability to purchase or sell holdings in a timely manner at a desired price. An inability to sell a portfolio holding can adversely affect the fund’s overall value or prevent the fund from being able to take advantage of other investment opportunities. Liquidity risk may be magnified during periods of substantial market volatility and unexpected episodes of illiquidity may limit the fund’s ability to pay redemption proceeds without selling holdings at an unfavorable time or at a suitable price. Large redemptions may also have a negative impact on the fund’s overall liquidity.

Active management The fund’s overall investment program and holdings selected by the fund’s investment adviser may underperform the broad markets, relevant indices, or other funds with similar objectives and investment strategies.

Cybersecurity breaches The fund could be harmed by intentional cyberattacks and other cybersecurity breaches, including unauthorized access to the fund’s assets, customer data and confidential shareholder information, or other proprietary information. In addition, a cybersecurity breach could cause one of the fund’s service providers or financial intermediaries to suffer unauthorized data access, data corruption, or loss of operational functionality.
Risk Lose Money [Text] rr_RiskLoseMoney The fund’s share price fluctuates, which means you could lose money by investing in the fund.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Performance
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock

The following performance information provides some indication of the risks of investing in the fund. The fund’s performance information represents only past performance (before and after taxes) and is not necessarily an indication of future results.

The following bar chart illustrates how much returns can differ from year to year by showing calendar year returns and the best and worst calendar quarter returns during those years for the fund’s Investor Class. Returns for other share classes vary since they have different expenses.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The following performance information provides some indication of the risks of investing in the fund. The following bar chart illustrates how much returns can differ from year to year by showing calendar year returns and the best and worst calendar quarter returns during those years for the fund’s Investor Class. Returns for other share classes vary since they have different expenses. The following table shows the average annual total returns for each class of the fund that has been in operation for at least one full calendar year, and also compares the returns with the returns of a relevant broad-based market index, as well as with the returns of one or more comparative indexes that have investment characteristics similar to those of the fund, if applicable.
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress troweprice.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture The fund’s performance information represents only past performance (before and after taxes) and is not necessarily an indication of future results.
Bar Chart [Heading] rr_BarChartHeading Calendar Year Returns
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock
                 
   

Quarter Ended

Total Return

    

Quarter Ended

Total Return

  
 

Best Quarter

6/30/20

37.59%

  

Worst Quarter

12/31/18

-17.04%

  
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns Periods ended December 31, 2020
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 an investor’s tax situation and may differ from those shown. After-tax returns shown are not relevant to investors who hold their fund shares through tax-deferred arrangements, such as a 401(k) account or an IRA.
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown After-tax returns are shown only for the Investor Class and will differ for other share classes.
Performance Table Narrative rr_PerformanceTableNarrativeTextBlock

The following table shows the average annual total returns for each class of the fund that has been in operation for at least one full calendar year, and also compares the returns with the returns of a relevant broad-based market index, as well as with the returns of one or more comparative indexes that have investment characteristics similar to those of the fund, if applicable.

In addition, the table shows hypothetical after-tax returns to demonstrate how taxes paid by a shareholder may influence returns. 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 an investor’s tax situation and may differ from those shown. After-tax returns shown are not relevant to investors who hold their fund shares through tax-deferred arrangements, such as a 401(k) account or an IRA. After-tax returns are shown only for the Investor Class and will differ for other share classes.
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock

Updated performance information is available through troweprice.com.
T. Rowe Price New Horizons Fund, Inc. | Russell 2000® Growth Index  
Risk/Return: rr_RiskReturnAbstract  
Index No Deduction for Fees, Expenses, Taxes [Text] rr_IndexNoDeductionForFeesExpensesTaxes reflects no deduction for fees, expenses, or taxes
Label rr_AverageAnnualReturnLabel Russell 2000 ® Growth Index (reflects no deduction for fees, expenses, or taxes)
T. Rowe Price New Horizons Fund, Inc. | Russell 2000® Growth Index  
Risk/Return: rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 34.63%
5 Years rr_AverageAnnualReturnYear05 16.36%
10 Years rr_AverageAnnualReturnYear10 13.48%
Since Inception rr_AverageAnnualReturnSinceInception 14.57% [1]
T. Rowe Price New Horizons Fund, Inc. | S&P 500 Index  
Risk/Return: rr_RiskReturnAbstract  
Index No Deduction for Fees, Expenses, Taxes [Text] rr_IndexNoDeductionForFeesExpensesTaxes reflects no deduction for fees, expenses, or taxes
Label rr_AverageAnnualReturnLabel S&P 500 Index (reflects no deduction for fees, expenses, or taxes)
T. Rowe Price New Horizons Fund, Inc. | S&P 500 Index  
Risk/Return: rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 18.40%
5 Years rr_AverageAnnualReturnYear05 15.22%
10 Years rr_AverageAnnualReturnYear10 13.88%
Since Inception rr_AverageAnnualReturnSinceInception 14.92% [1]
T. Rowe Price New Horizons Fund, Inc. | Lipper Mid-Cap Growth Funds Index  
Risk/Return: rr_RiskReturnAbstract  
Label rr_AverageAnnualReturnLabel Lipper Mid-Cap Growth Funds Index
T. Rowe Price New Horizons Fund, Inc. | Lipper Mid-Cap Growth Funds Index  
Risk/Return: rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 35.98%
5 Years rr_AverageAnnualReturnYear05 18.62%
10 Years rr_AverageAnnualReturnYear10 13.91%
Since Inception rr_AverageAnnualReturnSinceInception 16.87% [1]
T. Rowe Price New Horizons Fund, Inc. | Investor Class  
Risk/Return: rr_RiskReturnAbstract  
Maximum account fee rr_MaximumAccountFee $ 20 [2]
Management fees rr_ManagementFeesOverAssets 0.64%
Distribution and service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.11%
Total annual fund operating expenses rr_ExpensesOverAssets 0.75%
Fee waiver/expense reimbursement rr_FeeWaiverOrReimbursementOverAssets none
Total annual fund operating expenses after fee waiver/expense reimbursement rr_NetExpensesOverAssets 0.75%
1 Year rr_ExpenseExampleYear01 $ 77
3 Years rr_ExpenseExampleYear03 240
5 Years rr_ExpenseExampleYear05 417
10 Years rr_ExpenseExampleYear10 $ 930
Annual Return 2011 rr_AnnualReturn2011 6.63%
Annual Return 2012 rr_AnnualReturn2012 16.20%
Annual Return 2013 rr_AnnualReturn2013 49.11%
Annual Return 2014 rr_AnnualReturn2014 6.10%
Annual Return 2015 rr_AnnualReturn2015 4.50%
Annual Return 2016 rr_AnnualReturn2016 7.79%
Annual Return 2017 rr_AnnualReturn2017 31.49%
Annual Return 2018 rr_AnnualReturn2018 4.04%
Annual Return 2019 rr_AnnualReturn2019 37.71%
Annual Return 2020 rr_AnnualReturn2020 57.72%
Label rr_HighestQuarterlyReturnLabel Best Quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2020
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 37.59%
Label rr_LowestQuarterlyReturnLabel Worst Quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2018
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (17.04%)
1 Year rr_AverageAnnualReturnYear01 57.72%
5 Years rr_AverageAnnualReturnYear05 26.21%
10 Years rr_AverageAnnualReturnYear10 20.70%
Inception Date rr_AverageAnnualReturnInceptionDate Jun. 03, 1960
T. Rowe Price New Horizons Fund, Inc. | Investor Class | After Taxes on Distributions  
Risk/Return: rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 52.16%
5 Years rr_AverageAnnualReturnYear05 23.07%
10 Years rr_AverageAnnualReturnYear10 18.06%
T. Rowe Price New Horizons Fund, Inc. | Investor Class | After Taxes on Distributions and Sales  
Risk/Return: rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 36.33%
5 Years rr_AverageAnnualReturnYear05 20.53%
10 Years rr_AverageAnnualReturnYear10 16.64%
T. Rowe Price New Horizons Fund, Inc. | I Class  
Risk/Return: rr_RiskReturnAbstract  
Maximum account fee rr_MaximumAccountFee none
Management fees rr_ManagementFeesOverAssets 0.64%
Distribution and service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets none
Total annual fund operating expenses rr_ExpensesOverAssets 0.64%
Fee waiver/expense reimbursement rr_FeeWaiverOrReimbursementOverAssets none
Total annual fund operating expenses after fee waiver/expense reimbursement rr_NetExpensesOverAssets 0.64%
1 Year rr_ExpenseExampleYear01 $ 65
3 Years rr_ExpenseExampleYear03 205
5 Years rr_ExpenseExampleYear05 357
10 Years rr_ExpenseExampleYear10 $ 798
1 Year rr_AverageAnnualReturnYear01 57.92%
5 Years rr_AverageAnnualReturnYear05 26.37%
Since Inception rr_AverageAnnualReturnSinceInception 24.52%
Inception Date rr_AverageAnnualReturnInceptionDate Aug. 28, 2015
T. Rowe Price New Horizons Fund, Inc. | Z Class  
Risk/Return: rr_RiskReturnAbstract  
Maximum account fee rr_MaximumAccountFee none
Management fees rr_ManagementFeesOverAssets 0.64%
Distribution and service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets none
Total annual fund operating expenses rr_ExpensesOverAssets 0.64%
Fee waiver/expense reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.64%) [3]
Total annual fund operating expenses after fee waiver/expense reimbursement rr_NetExpensesOverAssets none [3]
1 Year rr_ExpenseExampleYear01 none
3 Years rr_ExpenseExampleYear03 none
5 Years rr_ExpenseExampleYear05 none
10 Years rr_ExpenseExampleYear10 none
Inception Date rr_AverageAnnualReturnInceptionDate Mar. 16, 2020
[1] Return since 8/28/15.
[2] Subject to certain exceptions, accounts with a balance of less than $10,000 are charged an annual $20 fee.
[3] T. Rowe Price Associates, Inc., has contractually agreed to waive and/or bear all the Z Class’ expenses (excluding interest; expenses related to borrowings, taxes, and brokerage; nonrecurring, extraordinary expenses; and acquired fund fees and expenses) in their entirety. T. Rowe Price Associates, Inc., expects this fee waiver and/or expense reimbursement arrangement to remain in place indefinitely, and the agreement may only be amended or terminated with approval by the fund’s Board of Directors.