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Risk/Return: rr_RiskReturnAbstract  
Registrant Name dei_EntityRegistrantName T. Rowe Price New Horizons Fund, Inc.
Prospectus Date rr_ProspectusDate May 01, 2016
Investor Class | T. Rowe Price New Horizons Fund, Inc.  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading T. Rowe Price

New Horizons Fund

SUMMARY
Objective [Heading] rr_ObjectiveHeading Investment Objective
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 and hold shares of the fund.
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption Fees and Expenses of the Fund

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 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 34.1% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 34.10%
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. 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 Investments, Risks, and Performance

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.
In pursuing its investment objective, the fund has the discretion to deviate from its normal investment criteria. These situations might arise when the fund’s adviser believes a security could increase in value for a variety of reasons, including an extraordinary corporate event, a new product introduction or innovation, a favorable competitive development, or a change in management.

The fund’s investments may include holdings in privately held companies and companies that only recently began to trade publicly. The fund may at times invest significantly in securities issued by technology companies. While most assets will typically be invested in U.S. common stocks, the fund may invest in foreign stocks in keeping with the fund’s objectives.

The fund may sell securities for a variety of reasons, such as to secure gains, limit losses, or redeploy assets into more promising opportunities.
Risk [Heading] rr_RiskHeading Principal Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock As with any mutual fund, there is no guarantee that the fund will achieve its objective. 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 are summarized as follows:

Active management risk The fund is subject to the risk that the investment adviser’s judgments about the attractiveness, value, or potential appreciation of the fund’s investments may prove to be incorrect. If the investments selected and strategies employed by the fund fail to produce the intended results, the fund could underperform in comparison to other funds with similar objectives and investment strategies.

Risks of 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 a stock in which the fund invests may decline due to general weakness in the stock market or because of factors that affect a particular company or industry.

Any investments in the stocks of privately held companies and newly public companies 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 generally considered to be illiquid and are 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 fund’s value may differ from the value assigned by other mutual funds holding the same security.

Investment style risk Different investment styles tend to shift in and out of favor depending on market conditions and investor sentiment. 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 capitalization risk Investing primarily in issuers within the same market capitalization category carries the risk that the category may be out of favor due to current market conditions or investor sentiment. Because the fund invests primarily in securities issued by small-cap companies, it is likely to be more volatile than a fund that focuses on securities issued by larger companies. Small-sized 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.

Industry risk To the extent the fund invests in specific industries or sectors, it may be more susceptible to developments affecting those industries and sectors. For example, the fund may at times have significant investments in technology companies, which could result in the fund performing poorly during a downturn in one or more of the industries that heavily impact technology companies. Technology companies can be adversely affected by, among other things, intense competition, earnings disappointments, and rapid obsolescence of products and services due to technological innovations or changing consumer preferences.

Foreign investing risk This is the risk that the fund’s investments in foreign securities 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.
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 bar chart showing calendar year returns and the average annual total returns table provide some indication of the risks of investing in the fund by showing how much returns can differ from year to year and how the fund’s average annual returns for certain periods compare 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. The fund’s performance information represents only past performance (before and after taxes) and is not necessarily an indication of future results.

The fund can also experience short-term performance swings, as shown by the best and worst calendar quarter returns during the years depicted.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The bar chart showing calendar year returns and the average annual total returns table provide some indication of the risks of investing in the fund by showing how much returns can differ from year to year and how the fund’s average annual returns for certain periods compare 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.
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 1-800-225-5132
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 New Horizons Fund
Calendar Year Returns
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock
  Quarter
 Ended		  Total
Return
Best Quarter   6/30/09  20.25%
Worst Quarter 12/31/08 -25.97%
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns

Periods ended
December 31, 2015
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 individual retirement account.
Performance Table Explanation after Tax Higher rr_PerformanceTableExplanationAfterTaxHigher In some cases, the figure shown for “returns after taxes on distributions and sale of fund shares” may be higher than the figure shown for “returns before taxes” because the calculations assume the investor received a tax deduction for any loss incurred on the sale of shares.
Performance Table Narrative rr_PerformanceTableNarrativeTextBlock In addition, the average annual total returns 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 individual retirement account. In some cases, the figure shown for “returns after taxes on distributions and sale of fund shares” may be higher than the figure shown for “returns before taxes” because the calculations assume the investor received a tax deduction for any loss incurred on the sale of shares.
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock Updated performance information is available through troweprice.com or may be obtained by calling 1-800-225-5132.
Investor Class | T. Rowe Price New Horizons Fund, Inc. | T. Rowe Price New Horizons Fund, Inc.  
Risk/Return: rr_RiskReturnAbstract  
Maximum sales charge (load) imposed on purchases rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum deferred sales charge (load) rr_MaximumDeferredSalesChargeOverOther none
Redemption fee rr_RedemptionFeeOverRedemption none
Maximum account fee rr_MaximumAccountFee $ 20 [1]
Management fees rr_ManagementFeesOverAssets 0.64%
Distribution and service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.15%
Total annual fund operating expenses rr_ExpensesOverAssets 0.79%
1 year rr_ExpenseExampleYear01 $ 81
3 years rr_ExpenseExampleYear03 252
5 years rr_ExpenseExampleYear05 439
10 years rr_ExpenseExampleYear10 $ 978
2006 rr_AnnualReturn2006 7.39%
2007 rr_AnnualReturn2007 6.25%
2008 rr_AnnualReturn2008 (38.78%)
2009 rr_AnnualReturn2009 43.87%
2010 rr_AnnualReturn2010 34.67%
2011 rr_AnnualReturn2011 6.63%
2012 rr_AnnualReturn2012 16.20%
2013 rr_AnnualReturn2013 49.11%
2014 rr_AnnualReturn2014 6.10%
2015 rr_AnnualReturn2015 4.50%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Best Quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2009
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 20.25%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Worst Quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2008
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (25.97%)
1 Year rr_AverageAnnualReturnYear01 4.50%
5 Years rr_AverageAnnualReturnYear05 15.42%
10 Years rr_AverageAnnualReturnYear10 10.73%
Investor Class | T. Rowe Price New Horizons Fund, Inc. | Returns after taxes on distributions | T. Rowe Price New Horizons Fund, Inc.  
Risk/Return: rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 2.71%
5 Years rr_AverageAnnualReturnYear05 13.26%
10 Years rr_AverageAnnualReturnYear10 9.28%
Investor Class | T. Rowe Price New Horizons Fund, Inc. | Returns after taxes on distributions and sale of fund shares | T. Rowe Price New Horizons Fund, Inc.  
Risk/Return: rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 4.01%
5 Years rr_AverageAnnualReturnYear05 12.27%
10 Years rr_AverageAnnualReturnYear10 8.69%
Investor Class | T. Rowe Price New Horizons Fund, Inc. | Russell 2000 Growth Index (reflects no deduction for fees, expenses, or taxes)  
Risk/Return: rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 (1.38%)
5 Years rr_AverageAnnualReturnYear05 10.67%
10 Years rr_AverageAnnualReturnYear10 7.95%
Investor Class | T. Rowe Price New Horizons Fund, Inc. | S&P 500 Index (reflects no deduction for fees, expenses, or taxes)  
Risk/Return: rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 1.38%
5 Years rr_AverageAnnualReturnYear05 12.57%
10 Years rr_AverageAnnualReturnYear10 7.31%
Investor Class | T. Rowe Price New Horizons Fund, Inc. | Russell 2000 Index (reflects no deduction for fees, expenses, or taxes)  
Risk/Return: rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 (4.41%)
5 Years rr_AverageAnnualReturnYear05 9.19%
10 Years rr_AverageAnnualReturnYear10 6.80%
[1] Subject to certain exceptions, accounts with a balance of less than $10,000 are charged an annual $20 fee.