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LORD ABBETT DEVELOPING GROWTH 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’s investment objective is long-term growth of capital through a diversified and actively managed portfolio consisting of developing growth companies, many of which are traded over the counter.
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 and certain members of your family invest, or agree to invest in the future, at least $50,000 in the Lord Abbett Family of Funds. More information about these and other discounts is available from your financial professional and in “Sales Charge Reductions and Waivers” on page 33 of the prospectus, Appendix A to the prospectus, titled “Intermediary-Specific Sales Charge Reductions and Waivers,” and “Purchases, Redemptions, Pricing, and Payments to Dealers” on page 9-1 of Part II of the statement of additional information (“SAI”).
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 Fund

shares are held in a taxable account. These costs, which are not reflected in the 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 122% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 122.00%
Expense Breakpoint Discounts [Text] rr_ExpenseBreakpointDiscounts You may qualify for sales charge discounts if you and certain members of your family invest, or agree to invest in the future, at least $50,000 in the Lord Abbett Family of Funds.
Expense Breakpoint, Minimum Investment Required [Amount] rr_ExpenseBreakpointMinimumInvestmentRequiredAmount $ 50,000
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. Class C shares automatically convert to Class A shares after eight years. The expense example for Class C shares for the ten-year period reflects the conversion to Class A shares. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Expense Example by, Year, Caption [Text] rr_ExpenseExampleByYearCaption If Shares Are Redeemed
Expense Example, No Redemption, By Year, Caption [Text] rr_ExpenseExampleNoRedemptionByYearCaption If Shares Are Not Redeemed
Strategy [Heading] rr_StrategyHeading PRINCIPAL INVESTMENT STRATEGIES
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock

The Fund invests in equity securities of companies that the portfolio management team believes demonstrate above-average, long-term growth potential. The portfolio management team seeks to identify companies that it believes are strongly positioned in the developing growth phase, which it defines as the period of swift development after a company’s start-up phase when growth is expected to occur at a rate generally not equaled by established companies in their mature years.

 

Under normal conditions, the Fund invests at least 65% of its net assets in equity securities of small companies. A small company is defined as a company having a market capitalization at the time of purchase that falls within the market capitalization range of companies in the Russell 2000® Index.

 

Equity securities in which the Fund may invest include common stocks, preferred stocks, equity interests in trusts (including real estate investment trusts and privately offered trusts), partnerships, joint ventures, limited liability companies and vehicles with similar legal structures, other instruments convertible or exercisable into the foregoing, and other investments with similar economic characteristics.

 

The Fund may invest up to 10% of its net assets in securities of foreign companies, including emerging market companies, American Depositary Receipts (“ADRs”), and other similar depositary receipts. In addition to ADRs, the Fund generally defines foreign companies as those whose securities are traded primarily on non-U.S. securities exchanges.

 

The Fund may engage in active and frequent trading of its portfolio securities.

 

The investment team may consider the risks and return potential presented by environmental, social, and governance (ESG) factors in investment decisions. The Fund may sell a security when the Fund believes the security is less likely to benefit from the current market and economic environment, or shows signs of deteriorating fundamentals, among other reasons. The Fund may deviate from the investment strategy described above for temporary defensive purposes. The Fund may miss certain investment opportunities if defensive strategies are used and thus may not achieve its investment objective.
Risk [Heading] rr_RiskHeading PRINCIPAL RISKS
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock

As with any investment in a mutual fund, investing in the Fund involves risk, including the risk that you may receive little or no return on your investment. When you redeem your shares, they may be worth more or less than what you paid for them, which means that you may lose a portion or all of the money you invested in

the Fund. The principal risks of investing in the Fund, which could adversely affect its performance, include:

 

●Portfolio Management Risk: If the strategies used and investments selected by the Fund’s portfolio management team fail to produce the intended result, the Fund may suffer losses or underperform other funds with the same investment objective or strategies, even in a favorable market.

 

●Market Risk: The market values of securities will fluctuate, sometimes sharply and unpredictably, based on overall economic conditions, governmental actions or intervention, market disruptions caused by trade disputes or other factors, political developments, and other factors. Prices of equity securities tend to rise and fall more dramatically than those of debt securities.

 

●Equity Securities Risk: Equity securities, as well as equity-like securities such as convertible debt securities, may experience significant volatility. Such securities may fall sharply in response to adverse events affecting overall markets, a particular industry or sector, or an individual company’s financial condition.

 

●Industry and Sector Risk: Although the Fund does not employ an industry or sector focus, its exposure to specific industries or sectors will increase from time to time based on the portfolio management team’s perception of investment opportunities. If the Fund overweights a single industry or sector relative to its benchmark index, the Fund will face an increased risk that the value of its portfolio will decrease because of events disproportionately affecting that industry or sector. Furthermore, investments in particular industries or sectors may be more volatile than the broader market as a whole.

 

●Mid-Sized and Small Company Risk: Investments in mid-sized and small companies may involve greater risks than investments in larger, more established companies. As compared to larger companies, mid-sized and small companies may have limited management experience or depth, limited ability to generate or borrow capital needed for growth, and limited products or services, or operate in less established markets. Accordingly, securities of mid-sized and small companies tend to be more sensitive to changing economic, market, and industry conditions and tend to be more volatile and less liquid than equity securities of larger companies, especially over the short term. The securities of mid-sized and small companies tend to trade less frequently than those of larger, more established companies, which can adversely affect the pricing of these securities and the ability to sell these securities in the future.

 

●Growth Investing Risk: Growth stocks typically trade at higher multiples of current earnings than other stocks. Growth stocks often are more sensitive to market fluctuations than other securities because their market prices are highly sensitive to future earnings expectations. At times when it appears that these expectations may not be met, prices of growth stocks typically fall. Growth stocks may be more volatile than securities of slower-growing issuers.
●Foreign and Emerging Market Company Risk: Investments in foreign companies and in U.S. companies with economic ties to foreign markets generally involve special risks that can increase the likelihood that the Fund will lose money. For example, as compared with companies organized and operated in the U.S., these companies may be more vulnerable to economic, political, and social instability and subject to less government supervision, lack of transparency, inadequate regulatory and accounting standards, and foreign taxes. In addition, the securities of foreign companies also may be subject to inadequate exchange control regulations, the imposition of economic sanctions or other government restrictions, higher transaction and other costs, reduced liquidity, and delays in settlement to the extent they are traded on non-U.S. exchanges or markets. Foreign company securities also include ADRs. ADRs may be less liquid than the underlying shares in their primary trading market. Foreign securities also may subject the Fund’s investments to changes in currency exchange rates. Emerging market securities generally are more volatile than other foreign securities, and are subject to greater liquidity, regulatory, and political risks. Investments in emerging markets may be considered speculative and generally are riskier than investments in more developed markets because such markets tend to develop unevenly and may never fully develop. Emerging markets are more likely to experience hyperinflation and currency devaluations. Securities of emerging market companies may have far lower trading volumes and less liquidity than securities of issuers in developed markets. Companies with economic ties to emerging markets may be susceptible to the same risks as companies organized in emerging markets.
   
●Foreign Currency Risk: Investments in securities denominated in foreign currencies are subject to the risk that those currencies will decline in value relative to the U.S. dollar, or, in the case of hedged positions, that the U.S. dollar will decline in value relative to the currency being hedged. Foreign currency exchange rates may fluctuate significantly over short periods of time.

 

●Liquidity/Redemption Risk: The Fund may lose money when selling securities at inopportune times to fulfill shareholder redemption requests. The risk of loss may increase depending on the size and frequency of redemption requests, whether the redemption requests occur in times of overall market turmoil or declining prices, and whether the securities the Fund intends to sell have decreased in value or are illiquid. The Fund may be less able to sell illiquid securities at its desired time or price. It may be more difficult for the Fund to value its investments in illiquid securities than more liquid securities.

 

●High Portfolio Turnover Risk: High portfolio turnover may result in increased transaction costs, reduced investment performance, and higher taxes resulting from increased realized capital gains, including short-term capital gains taxable as ordinary income when distributed to shareholders.

 

An investment in the Fund is not a deposit of any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government

agency. For more information on the principal risks of the Fund, please see the “More Information About the Fund – Principal Risks” section in the prospectus.
Risk Lose Money [Text] rr_RiskLoseMoney As with any investment in a mutual fund, investing in the Fund involves risk, including the risk that you may receive little or no return on your investment. When you redeem your shares, they may be worth more or less than what you paid for them, which means that you may lose a portion or all of the money you invested in the Fund.
RIsk Not Insured [Text] rr_RiskNotInsured An investment in the Fund is not a deposit of any 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 Narrative [Text Block] rr_PerformanceNarrativeTextBlock

The bar chart and table below provide some indication of the risks of investing in the Fund by illustrating the variability of the Fund’s returns. Each assumes reinvestment of dividends and distributions. The Fund’s past performance, before and after taxes, is not necessarily an indication of how the Fund will perform in the future. Furthermore, high double-digit returns were achieved primarily during favorable market conditions and may not be repeated in the future.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The bar chart and table below provide some indication of the risks of investing in the Fund by illustrating the variability of the Fund’s returns.
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 888-522-2388
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress www.lordabbett.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 Bar Chart (per calendar year) - Class A Shares*
Bar Chart Narrative [Text Block] rr_BarChartNarrativeTextBlock

The bar chart shows changes in the performance of the Fund’s Class A shares from calendar year to calendar year. This chart does not reflect the sales charge applicable to Class A shares. If the sales charge were reflected, returns would be lower. Performance for the Fund’s other share classes will vary due to the different expenses each class bears. Updated performance information is available at www.lordabbett.com or by calling 888-522-2388.
Bar Chart Does Not Reflect Sales Loads [Text] rr_BarChartDoesNotReflectSalesLoads This chart does not reflect the sales charge applicable to Class A shares. If the sales charge were reflected, returns would be lower.
Bar Chart Footnotes [Text Block] rr_BarChartFootnotesTextBlock

* The total return for the Fund’s Class A shares for the nine-month period from January 1, 2020 to September 30, 2020 was 35.40%.
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock

Best Quarter 1st Q ‘19 +27.01%

Worst Quarter 4th Q ‘18 -23.96%
Year to Date Return, Label rr_YearToDateReturnLabel The total return for the Fund’s Class A shares for the nine-month period from January 1, 2020 to September 30, 2020 was 35.40%.
Bar Chart, Year to Date Return, Date rr_BarChartYearToDateReturnDate Sep. 30, 2020
Bar Chart, Year to Date Return rr_BarChartYearToDateReturn 35.40%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Best Quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Mar. 31, 2019
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 27.01%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Worst Quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2018
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (23.96%)
Performance Table Does Reflect Sales Loads rr_PerformanceTableDoesReflectSalesLoads The Fund’s average annual total returns include applicable sales charges.
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 The after-tax returns of Class A shares included in the table below 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 The after-tax returns shown are not relevant to investors who hold their Fund shares through tax-advantaged arrangements such as 401(k) plans or Individual Retirement Accounts (“IRAs”).
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown After-tax returns for other share classes are not shown in the table and will vary from those shown for Class A shares.
Performance Table Explanation after Tax Higher rr_PerformanceTableExplanationAfterTaxHigher In some cases, the return after taxes on distributions and sale of Fund shares may exceed the return before taxes due to a tax benefit resulting from realized losses on a sale of Fund shares at the end of the period that is used to offset other gains.
Performance Table Narrative rr_PerformanceTableNarrativeTextBlock

The table below shows how the Fund’s average annual total returns compare to the returns of a securities market index with investment characteristics similar to those of the Fund. The Fund’s average annual total returns include applicable sales charges.

 

The after-tax returns of Class A shares included in the table below are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. In some cases, the return after taxes on distributions and sale of Fund shares may exceed the return before taxes due to a tax

benefit resulting from realized losses on a sale of Fund shares at the end of the period that is used to offset other gains. Actual after-tax returns depend on an investor’s tax situation and may differ from those shown. The after-tax returns shown are not relevant to investors who hold their Fund shares through tax-advantaged arrangements such as 401(k) plans or Individual Retirement Accounts (“IRAs”). After-tax returns for other share classes are not shown in the table and will vary from those shown for Class A shares.
Average Annual Return, Caption rr_AverageAnnualReturnCaption Average Annual Total Returns   (for the periods ended December 31, 2019)
LORD ABBETT DEVELOPING GROWTH FUND INC | Class A  
Risk/Return: rr_RiskReturnAbstract  
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 5.75% [1]
Maximum Deferred Sales Charge (Load) (as a percentage of offering price or redemption proceeds, whichever is lower) rr_MaximumDeferredSalesChargeOverOfferingPrice none [1],[2]
Management Fees rr_ManagementFeesOverAssets 0.51%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses rr_OtherExpensesOverAssets 0.17%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.93%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 664
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 854
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 1,060
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 1,652
Expense Example, No Redemption, 1 Year rr_ExpenseExampleNoRedemptionYear01 664
Expense Example, No Redemption, 3 Years rr_ExpenseExampleNoRedemptionYear03 854
Expense Example, No Redemption, 5 Years rr_ExpenseExampleNoRedemptionYear05 1,060
Expense Example, No Redemption, 10 Years rr_ExpenseExampleNoRedemptionYear10 $ 1,652
Annual Return 2010 rr_AnnualReturn2010 36.54%
Annual Return 2011 rr_AnnualReturn2011 (1.66%)
Annual Return 2012 rr_AnnualReturn2012 10.39%
Annual Return 2013 rr_AnnualReturn2013 57.19%
Annual Return 2014 rr_AnnualReturn2014 3.25%
Annual Return 2015 rr_AnnualReturn2015 (8.90%)
Annual Return 2016 rr_AnnualReturn2016 (2.71%)
Annual Return 2017 rr_AnnualReturn2017 29.92%
Annual Return 2018 rr_AnnualReturn2018 5.09%
Annual Return 2019 rr_AnnualReturn2019 31.91%
1 Year rr_AverageAnnualReturnYear01 24.36%
5 Years rr_AverageAnnualReturnYear05 8.52%
10 Years rr_AverageAnnualReturnYear10 13.73%
LORD ABBETT DEVELOPING GROWTH FUND INC | Class A | After Taxes on Distributions  
Risk/Return: rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 18.64%
5 Years rr_AverageAnnualReturnYear05 5.72%
10 Years rr_AverageAnnualReturnYear10 10.90%
LORD ABBETT DEVELOPING GROWTH FUND INC | Class A | After Taxes on Distributions and Sale of Fund Shares  
Risk/Return: rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 18.17%
5 Years rr_AverageAnnualReturnYear05 6.28%
10 Years rr_AverageAnnualReturnYear10 10.74%
LORD ABBETT DEVELOPING GROWTH FUND INC | Class C  
Risk/Return: rr_RiskReturnAbstract  
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none [1]
Maximum Deferred Sales Charge (Load) (as a percentage of offering price or redemption proceeds, whichever is lower) rr_MaximumDeferredSalesChargeOverOfferingPrice 1.00% [1],[3]
Management Fees rr_ManagementFeesOverAssets 0.51%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 1.00%
Other Expenses rr_OtherExpensesOverAssets 0.17%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.68%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 271
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 530
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 913
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 1,788
Expense Example, No Redemption, 1 Year rr_ExpenseExampleNoRedemptionYear01 171
Expense Example, No Redemption, 3 Years rr_ExpenseExampleNoRedemptionYear03 530
Expense Example, No Redemption, 5 Years rr_ExpenseExampleNoRedemptionYear05 913
Expense Example, No Redemption, 10 Years rr_ExpenseExampleNoRedemptionYear10 $ 1,788
1 Year rr_AverageAnnualReturnYear01 29.96%
5 Years rr_AverageAnnualReturnYear05 8.97%
10 Years rr_AverageAnnualReturnYear10 13.59%
LORD ABBETT DEVELOPING GROWTH FUND INC | Class F  
Risk/Return: rr_RiskReturnAbstract  
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none [1]
Maximum Deferred Sales Charge (Load) (as a percentage of offering price or redemption proceeds, whichever is lower) rr_MaximumDeferredSalesChargeOverOfferingPrice none [1]
Management Fees rr_ManagementFeesOverAssets 0.51%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.10%
Other Expenses rr_OtherExpensesOverAssets 0.17%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.78%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 80
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 249
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 433
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 966
Expense Example, No Redemption, 1 Year rr_ExpenseExampleNoRedemptionYear01 80
Expense Example, No Redemption, 3 Years rr_ExpenseExampleNoRedemptionYear03 249
Expense Example, No Redemption, 5 Years rr_ExpenseExampleNoRedemptionYear05 433
Expense Example, No Redemption, 10 Years rr_ExpenseExampleNoRedemptionYear10 $ 966
1 Year rr_AverageAnnualReturnYear01 32.14%
5 Years rr_AverageAnnualReturnYear05 9.98%
10 Years rr_AverageAnnualReturnYear10 14.63%
LORD ABBETT DEVELOPING GROWTH FUND INC | Class F3  
Risk/Return: rr_RiskReturnAbstract  
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none [1]
Maximum Deferred Sales Charge (Load) (as a percentage of offering price or redemption proceeds, whichever is lower) rr_MaximumDeferredSalesChargeOverOfferingPrice none [1]
Management Fees rr_ManagementFeesOverAssets 0.51%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses rr_OtherExpensesOverAssets 0.08%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.59%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 60
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 189
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 329
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 738
Expense Example, No Redemption, 1 Year rr_ExpenseExampleNoRedemptionYear01 60
Expense Example, No Redemption, 3 Years rr_ExpenseExampleNoRedemptionYear03 189
Expense Example, No Redemption, 5 Years rr_ExpenseExampleNoRedemptionYear05 329
Expense Example, No Redemption, 10 Years rr_ExpenseExampleNoRedemptionYear10 $ 738
1 Year rr_AverageAnnualReturnYear01 32.39%
Life of Class rr_AverageAnnualReturnSinceInception 21.14%
Inception Date for Performance rr_AverageAnnualReturnInceptionDate Apr. 04, 2017
LORD ABBETT DEVELOPING GROWTH FUND INC | Class F3 | Russell 2000® Growth Index (reflects no deduction for fees, expenses, or taxes)  
Risk/Return: rr_RiskReturnAbstract  
Life of Class rr_AverageAnnualReturnSinceInception 12.19%
Inception Date for Performance rr_AverageAnnualReturnInceptionDate Apr. 04, 2017
LORD ABBETT DEVELOPING GROWTH FUND INC | Class I  
Risk/Return: rr_RiskReturnAbstract  
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none [1]
Maximum Deferred Sales Charge (Load) (as a percentage of offering price or redemption proceeds, whichever is lower) rr_MaximumDeferredSalesChargeOverOfferingPrice none [1]
Management Fees rr_ManagementFeesOverAssets 0.51%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses rr_OtherExpensesOverAssets 0.17%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.68%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 69
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 218
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 379
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 847
Expense Example, No Redemption, 1 Year rr_ExpenseExampleNoRedemptionYear01 69
Expense Example, No Redemption, 3 Years rr_ExpenseExampleNoRedemptionYear03 218
Expense Example, No Redemption, 5 Years rr_ExpenseExampleNoRedemptionYear05 379
Expense Example, No Redemption, 10 Years rr_ExpenseExampleNoRedemptionYear10 $ 847
1 Year rr_AverageAnnualReturnYear01 32.25%
5 Years rr_AverageAnnualReturnYear05 10.09%
10 Years rr_AverageAnnualReturnYear10 14.75%
LORD ABBETT DEVELOPING GROWTH FUND INC | Class P  
Risk/Return: rr_RiskReturnAbstract  
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none [1]
Maximum Deferred Sales Charge (Load) (as a percentage of offering price or redemption proceeds, whichever is lower) rr_MaximumDeferredSalesChargeOverOfferingPrice none [1]
Management Fees rr_ManagementFeesOverAssets 0.51%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.45%
Other Expenses rr_OtherExpensesOverAssets 0.17%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.13%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 115
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 359
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 622
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 1,375
Expense Example, No Redemption, 1 Year rr_ExpenseExampleNoRedemptionYear01 115
Expense Example, No Redemption, 3 Years rr_ExpenseExampleNoRedemptionYear03 359
Expense Example, No Redemption, 5 Years rr_ExpenseExampleNoRedemptionYear05 622
Expense Example, No Redemption, 10 Years rr_ExpenseExampleNoRedemptionYear10 $ 1,375
1 Year rr_AverageAnnualReturnYear01 31.72%
5 Years rr_AverageAnnualReturnYear05 9.75%
10 Years rr_AverageAnnualReturnYear10 14.36%
LORD ABBETT DEVELOPING GROWTH FUND INC | Class R2  
Risk/Return: rr_RiskReturnAbstract  
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none [1]
Maximum Deferred Sales Charge (Load) (as a percentage of offering price or redemption proceeds, whichever is lower) rr_MaximumDeferredSalesChargeOverOfferingPrice none [1]
Management Fees rr_ManagementFeesOverAssets 0.51%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.60%
Other Expenses rr_OtherExpensesOverAssets 0.17%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.28%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 130
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 406
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 702
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 1,545
Expense Example, No Redemption, 1 Year rr_ExpenseExampleNoRedemptionYear01 130
Expense Example, No Redemption, 3 Years rr_ExpenseExampleNoRedemptionYear03 406
Expense Example, No Redemption, 5 Years rr_ExpenseExampleNoRedemptionYear05 702
Expense Example, No Redemption, 10 Years rr_ExpenseExampleNoRedemptionYear10 $ 1,545
1 Year rr_AverageAnnualReturnYear01 31.47%
5 Years rr_AverageAnnualReturnYear05 9.43%
10 Years rr_AverageAnnualReturnYear10 14.06%
LORD ABBETT DEVELOPING GROWTH FUND INC | Class R3  
Risk/Return: rr_RiskReturnAbstract  
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none [1]
Maximum Deferred Sales Charge (Load) (as a percentage of offering price or redemption proceeds, whichever is lower) rr_MaximumDeferredSalesChargeOverOfferingPrice none [1]
Management Fees rr_ManagementFeesOverAssets 0.51%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.50%
Other Expenses rr_OtherExpensesOverAssets 0.17%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.18%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 120
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 375
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 649
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 1,432
Expense Example, No Redemption, 1 Year rr_ExpenseExampleNoRedemptionYear01 120
Expense Example, No Redemption, 3 Years rr_ExpenseExampleNoRedemptionYear03 375
Expense Example, No Redemption, 5 Years rr_ExpenseExampleNoRedemptionYear05 649
Expense Example, No Redemption, 10 Years rr_ExpenseExampleNoRedemptionYear10 $ 1,432
1 Year rr_AverageAnnualReturnYear01 31.63%
5 Years rr_AverageAnnualReturnYear05 9.54%
10 Years rr_AverageAnnualReturnYear10 14.17%
LORD ABBETT DEVELOPING GROWTH FUND INC | Class R4  
Risk/Return: rr_RiskReturnAbstract  
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none [1]
Maximum Deferred Sales Charge (Load) (as a percentage of offering price or redemption proceeds, whichever is lower) rr_MaximumDeferredSalesChargeOverOfferingPrice none [1]
Management Fees rr_ManagementFeesOverAssets 0.51%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses rr_OtherExpensesOverAssets 0.17%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.93%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 95
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 296
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 515
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 1,143
Expense Example, No Redemption, 1 Year rr_ExpenseExampleNoRedemptionYear01 95
Expense Example, No Redemption, 3 Years rr_ExpenseExampleNoRedemptionYear03 296
Expense Example, No Redemption, 5 Years rr_ExpenseExampleNoRedemptionYear05 515
Expense Example, No Redemption, 10 Years rr_ExpenseExampleNoRedemptionYear10 $ 1,143
1 Year rr_AverageAnnualReturnYear01 31.99%
Life of Class rr_AverageAnnualReturnSinceInception 8.64%
Inception Date for Performance rr_AverageAnnualReturnInceptionDate Jun. 30, 2015
LORD ABBETT DEVELOPING GROWTH FUND INC | Class R4 | Russell 2000® Growth Index (reflects no deduction for fees, expenses, or taxes)  
Risk/Return: rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 28.48%
5 Years rr_AverageAnnualReturnYear05 9.34%
10 Years rr_AverageAnnualReturnYear10 13.01%
Life of Class rr_AverageAnnualReturnSinceInception 8.39%
Inception Date for Performance rr_AverageAnnualReturnInceptionDate Jun. 30, 2015
LORD ABBETT DEVELOPING GROWTH FUND INC | Class R5  
Risk/Return: rr_RiskReturnAbstract  
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none [1]
Maximum Deferred Sales Charge (Load) (as a percentage of offering price or redemption proceeds, whichever is lower) rr_MaximumDeferredSalesChargeOverOfferingPrice none [1]
Management Fees rr_ManagementFeesOverAssets 0.51%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses rr_OtherExpensesOverAssets 0.17%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.68%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 69
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 218
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 379
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 847
Expense Example, No Redemption, 1 Year rr_ExpenseExampleNoRedemptionYear01 69
Expense Example, No Redemption, 3 Years rr_ExpenseExampleNoRedemptionYear03 218
Expense Example, No Redemption, 5 Years rr_ExpenseExampleNoRedemptionYear05 379
Expense Example, No Redemption, 10 Years rr_ExpenseExampleNoRedemptionYear10 $ 847
1 Year rr_AverageAnnualReturnYear01 32.31%
Life of Class rr_AverageAnnualReturnSinceInception 8.92%
Inception Date for Performance rr_AverageAnnualReturnInceptionDate Jun. 30, 2015
LORD ABBETT DEVELOPING GROWTH FUND INC | Class R6  
Risk/Return: rr_RiskReturnAbstract  
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none [1]
Maximum Deferred Sales Charge (Load) (as a percentage of offering price or redemption proceeds, whichever is lower) rr_MaximumDeferredSalesChargeOverOfferingPrice none [1]
Management Fees rr_ManagementFeesOverAssets 0.51%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses rr_OtherExpensesOverAssets 0.08%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.59%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 60
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 189
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 329
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 738
Expense Example, No Redemption, 1 Year rr_ExpenseExampleNoRedemptionYear01 60
Expense Example, No Redemption, 3 Years rr_ExpenseExampleNoRedemptionYear03 189
Expense Example, No Redemption, 5 Years rr_ExpenseExampleNoRedemptionYear05 329
Expense Example, No Redemption, 10 Years rr_ExpenseExampleNoRedemptionYear10 $ 738
1 Year rr_AverageAnnualReturnYear01 32.40%
Life of Class rr_AverageAnnualReturnSinceInception 9.04%
Inception Date for Performance rr_AverageAnnualReturnInceptionDate Jun. 30, 2015
[1] A shareholder transacting in share classes without a front-end sales charge may be required to pay a commission to its financial intermediary. Please contact your financial intermediary for more information about whether such a commission may apply to your transaction.
[2] A contingent deferred sales charge (“CDSC”) of 1.00% may be assessed on certain Class A shares purchased or acquired without a sales charge if they are redeemed before the first day of the month of the one-year anniversary of the purchase.
[3] A CDSC of 1.00% may be assessed on Class C shares if they are redeemed before the first anniversary of their purchase.