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Risk/Return: rr_RiskReturnAbstract  
Registrant Name dei_EntityRegistrantName JANUS INVESTMENT FUND
Prospectus Date rr_ProspectusDate Oct. 26, 2012
Perkins Mid Cap Value Fund | Class A, C, S, I, N, R, T Shares
  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading Fund summary

Perkins Mid Cap Value Fund
Objective [Heading] rr_ObjectiveHeading INVESTMENT OBJECTIVE
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock Perkins Mid Cap Value Fund seeks capital appreciation.
Expense [Heading] rr_ExpenseHeading FEES AND EXPENSES OF THE FUND
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. Each share class has different expenses, but represents an investment in the same Fund.
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)
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination November 1, 2013
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 54% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 54.00%
Expense Breakpoint Discounts [Text] rr_ExpenseBreakpointDiscounts For Class A Shares, you may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in the Fund or in other Janus mutual funds. More information about these and other discounts, as well as eligibility requirements for each share class, is available from your financial professional and in the “Purchases” section on page 60 of the Fund’s Prospectus and in the “Purchases” section on page 83 of the Fund’s Statement of Additional Information.
Expense Breakpoint, Minimum Investment Required [Amount] rr_ExpenseBreakpointMinimumInvestmentRequiredAmount 50,000
Expense Example [Heading] rr_ExpenseExampleHeading EXAMPLE:
Expense Example by Year [Heading] rr_ExpenseExampleByYearHeading The Example assumes that you invest $10,000 in the Fund for the time periods indicated and reinvest all dividends and distributions. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses without waivers remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock The following Example is based on expenses without waivers. The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.
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 pursues its investment objective by investing primarily in common stocks selected for their capital appreciation potential. The Fund primarily invests in the common stocks of mid-sized companies whose stock prices the portfolio managers believe to be undervalued. The Fund invests, under normal circumstances, at least 80% of its net assets in equity securities of companies whose market capitalization falls, at the time of purchase, within the 12-month average of the capitalization range of the Russell Midcap® Value Index. This average is updated monthly. The market capitalizations within the index will vary, but as of June 30, 2012, they ranged from approximately $1.3 billion to $18.5 billion. The Fund may also invest in foreign equity and debt securities, which may include investments in emerging markets. The Fund may invest, under normal circumstances, up to 20% of its net assets in securities of companies having market capitalizations outside of the aforementioned market capitalization ranges. In addition, when the portfolio managers believe that market conditions are unfavorable for investing, or when they are otherwise unable to locate attractive investment opportunities, the Fund may invest up to 20% of its net assets in cash or similar investments.

The Fund focuses on companies that have fallen out of favor with the market or that appear to be temporarily misunderstood by the investment community. The Fund’s portfolio managers generally look for companies with:
  •   strong balance sheets and solid recurring free cash flows
  •   attractive relative and absolute valuation ratios or that have underperformed recently
  •   favorable reward to risk characteristics
The Fund may also invest its assets in derivatives, which are instruments that have a value derived from or directly linked to an underlying asset, such as equity securities, bonds, commodities, currencies, interest rates, or market indices. The Fund has and is expected to continue to buy and sell put and call options, particularly on market indices, for hedging purposes (to offset risks associated with an investment, currency exposure, or market conditions) and to enhance returns. The Fund’s exposure to derivatives will vary, is not limited to those derivatives listed, and could be significant at times. For purposes of meeting its 80% investment policy, the Fund may include derivatives that have characteristics similar to the Fund’s direct investments. For more information on the Fund’s use of derivatives, refer to the Fund’s shareholder reports and Form N-Q reports, which are filed with the Securities and Exchange Commission.
Risk [Heading] rr_RiskHeading PRINCIPAL INVESTMENT RISKS
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock The biggest risk is that the Fund’s returns will vary, and you could lose money. The Fund is designed for long-term investors seeking an equity portfolio, including common stocks. Common stocks tend to be more volatile than many other investment choices.

Value Investing Risk. Because different types of stocks tend to shift in and out of favor depending on market and economic conditions, “value” stocks may perform differently than other types of stocks and from the market as a whole, and can continue to be undervalued by the market for long periods of time. It is also possible that a value stock will never appreciate to the extent expected by the Fund’s portfolio managers. When the Fund’s investments in cash or similar investments increase due to a lack of favorable investment opportunities or other extraordinary factors, the Fund may not participate in market advances or declines to the same extent that it would if the Fund had been fully invested.

Market Risk. The value of the Fund’s portfolio may decrease if the value of an individual company or security, or multiple companies or securities, in the portfolio decreases or if the portfolio managers’ belief about a company’s intrinsic worth is incorrect. Further, regardless of how well individual companies or securities perform, the value of the Fund’s portfolio could also decrease if there are deteriorating economic or market conditions. It is important to understand that the value of your investment may fall, sometimes sharply, in response to changes in the market, and you could lose money.

Mid-Sized Companies Risk. The Fund’s investments in securities issued by mid-sized companies may involve greater risks than are customarily associated with larger, more established companies. Securities issued by mid-sized companies tend to be more volatile than securities issued by larger or more established companies and may underperform as compared to the securities of larger companies.

Foreign Exposure Risk. The Fund may have exposure to foreign markets as a result of its investments in foreign securities, including investments in emerging markets, which can be more volatile than the U.S. markets. As a result, its returns and net asset value may be affected to a large degree by fluctuations in currency exchange rates or political or economic conditions in a particular country. In some foreign markets, there may not be protection against failure by other parties to complete transactions. It may not be possible for the Fund to repatriate capital, dividends, interest, and other income from a particular country or governmental entity. In addition, a market swing in one or more countries or regions where the Fund has invested a significant amount of its assets may have a greater effect on the Fund’s performance than it would in a more geographically diversified portfolio.

Derivatives Risk. Derivatives can be highly volatile and involve risks in addition to the risks of the underlying referenced securities. Gains or losses from a derivative can be substantially greater than the derivative’s original cost, and can therefore involve leverage. Derivatives can be complex instruments and may involve analysis that differs from that required for other investment types used by the Fund. If the value of a derivative does not correlate well with the particular market or other asset class to which the derivative is intended to provide exposure, the derivative may not produce the anticipated result. Derivatives can also reduce the opportunity for gain or result in losses by offsetting positive returns in other investments. Derivatives can be less liquid than other types of investments and entail the risk that the counterparty will default on its payment obligations. If the counterparty to a derivative transaction defaults, the Fund would risk the loss of the net amount of the payments that it contractually is entitled to receive. To the extent the Fund enters into short derivative positions, the Fund may be exposed to risks similar to those associated with short sales, including the risk that the Fund’s losses are theoretically unlimited.

Real Estate Risk. The Fund may be affected by risks associated with investments in real estate-related securities. The value of securities of issuers in the real estate and real estate-related industries, including real estate investment trusts, is sensitive to changes in real estate values and rental income, property taxes, interest rates, tax and regulatory requirements, supply and demand, and the management skill and creditworthiness of the issuer. These factors may impact the Fund’s investments in foreign real estate markets differently than U.S. real estate markets.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Risk Lose Money [Text] rr_RiskLoseMoney The biggest risk is that the Fund’s returns will vary, and you could lose money.
Risk Not Insured Depository Institution [Text] rr_RiskNotInsuredDepositoryInstitution An investment in the Fund is not a bank deposit 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 INFORMATION
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class T Shares (formerly named Class J Shares) of the Fund commenced operations with the Fund’s inception. Class A Shares, Class C Shares, Class S Shares, Class I Shares, and Class R Shares of the Fund commenced operations on July 6, 2009. Class N Shares of the Fund commenced operations on May 31, 2012.
  •  The performance shown for Class T Shares for periods following April 21, 2003, reflects the fees and expenses of Class T Shares in effect during the periods shown, net of any applicable fee and expense limitations or waivers. For the periods prior to April 21, 2003, the performance shown for Class T Shares reflects the historical performance of Berger Mid Cap Value Fund – Investor Shares (as a result of a prior reorganization of Berger Mid Cap Value Fund – Investor Shares into the Fund’s former Class J Shares).
  •  The performance shown for Class A Shares, Class C Shares, Class S Shares, and Class R Shares reflects the performance of the Fund’s Class J Shares (formerly named Investor Shares) from April 21, 2003 to July 6, 2009, calculated using the fees and expenses of each respective share class, without the effect of any fee and expense limitations or waivers. For periods prior to April 21, 2003, the performance shown for Class A Shares, Class C Shares, Class S Shares, and Class R Shares reflects the historical performance of Berger Mid Cap Value Fund – Investor Shares (as a result of a prior reorganization of Berger Mid Cap Value Fund – Investor Shares into the Fund’s former Class J Shares), calculated using the fees and expenses of each respective share class, without the effect of any fee and expense limitations or waivers.
  •  The performance shown for Class I Shares reflects the performance of the Fund’s Class J Shares (formerly named Investor Shares) from April 21, 2003 to July 6, 2009, calculated using the fees and expenses of Class J Shares, net of any applicable fee and expense limitations or waivers. For the periods prior to April 21, 2003, the performance shown for Class I Shares reflects the historical performance of Berger Mid Cap Value Fund – Investor Shares (as a result of a prior reorganization of Berger Mid Cap Value Fund – Investor Shares into the Fund’s former Class J Shares), calculated using the fees and expenses of Class J Shares, net of any applicable fee and expense limitations or waivers.
  •  The performance shown for Class N Shares reflects the performance of the Fund’s Class T Shares from July 6, 2009 to December 31, 2011, calculated using the fees and expenses of Class T Shares, net of any applicable fee and expense limitations or waivers. For the period from April 21, 2003 to July 6, 2009, the performance shown for Class N Shares reflects the performance of the Fund’s Class J Shares (formerly named Investor Shares), calculated using the fees and expenses of Class J Shares, net of any applicable fee and expense limitations or waivers. For the periods prior to April 21, 2003, the performance shown for Class N Shares reflects the historical performance of Berger Mid Cap Value Fund – Investor Shares (as a result of a prior reorganization of Berger Mid Cap Value Fund – Investor Shares into the Fund’s former Class J Shares), calculated using the fees and expenses of Class J Shares, net of any applicable fee and expense limitations or waivers.
If Class A Shares, Class C Shares, Class S Shares, Class I Shares, and Class R Shares of the Fund had been available during periods prior to July 6, 2009, or Class N Shares of the Fund had been available during periods prior to December 31, 2011, the performance shown for each respective share class may have been different. The performance shown for periods following the Fund’s commencement of Class A Shares, Class C Shares, Class S Shares, Class I Shares, Class N Shares, and Class R Shares reflects the fees and expenses of each respective share class, net of any applicable fee and expense limitations or waivers.

The bar chart depicts the change in performance from year to year during the periods indicated. The bar chart figures do not include any applicable sales charges that an investor may pay when they buy or sell Class A Shares or Class C Shares of the Fund. If sales charges were included, the returns would be lower. The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time.

The bar chart depicts the change in performance from year to year during the periods indicated.
Performance Additional Market Index [Text] rr_PerformanceAdditionalMarketIndex The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions.
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 1-877-335-2687
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress janus.com/advisor/mutual-funds
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.
Bar Chart [Heading] rr_BarChartHeading Annual Total Returns for Class T Shares (calendar year-end)
Bar Chart Does Not Reflect Sales Loads [Text] rr_BarChartDoesNotReflectSalesLoads The bar chart figures do not include any applicable sales charges that an investor may pay when they buy or sell Class A Shares or Class C Shares of the Fund. If sales charges were included, the returns would be lower.
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock
Best Quarter: Second Quarter 2003 17.17%           Worst Quarter: Fourth Quarter 2008 −19.63%
Year to Date Return, Label rr_YearToDateReturnLabel The Fund’s year-to-date return as of the calendar quarter ended September 30, 2012 was 9.06%.
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns (periods ended 12/31/11)
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate After-tax returns are calculated using the historically 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 your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown After-tax returns are only shown for Class T Shares of the Fund. After-tax returns for the other classes of Shares will vary from those shown for Class T Shares due to varying sales charges (as applicable), fees, and expenses among the classes.
Performance Table Explanation after Tax Higher rr_PerformanceTableExplanationAfterTaxHigher If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund’s other return figures.
Performance Table Narrative rr_PerformanceTableNarrativeTextBlock After-tax returns are calculated using distributions for the Fund’s Class T Shares (formerly named Class J Shares) for the periods following April 21, 2003; and for Berger Mid Cap Value Fund – Investor Shares for periods prior to April 21, 2003. If Class T Shares of the Fund had been available during the periods prior to April 21, 2003, distributions may have been different and thus, after-tax returns may have been different from those shown. After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

After-tax returns are only shown for Class T Shares of the Fund. After-tax returns for the other classes of Shares will vary from those shown for Class T Shares due to varying sales charges (as applicable), fees, and expenses among the classes.
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.
Perkins Mid Cap Value Fund | Class A, C, S, I, N, R, T Shares | Class A
  
Risk/Return: rr_RiskReturnAbstract  
Shareholder Fees Column [Text] rr_ShareholderFeesColumnName Class A
Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 5.75%
Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds) rr_MaximumDeferredSalesChargeOverOther none
Operating Expenses Column [Text] rr_OperatingExpensesColumnName Class A
Management Fees (may adjust up or down) rr_ManagementFeesOverAssets 0.54%
Distribution/Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses rr_OtherExpensesOverAssets 0.26%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.05% [1]
Fee Waiver rr_FeeWaiverOrReimbursementOverAssets 0.04% [1]
Total Annual Fund Operating Expenses After Fee Waiver rr_NetExpensesOverAssets 1.01% [1]
Expense Example, By Year, Column [Text] rr_ExpenseExampleByYearColumnName Class A Shares
1 Year rr_ExpenseExampleYear01 676
3 Years rr_ExpenseExampleYear03 890
5 Years rr_ExpenseExampleYear05 1,121
10 Years rr_ExpenseExampleYear10 1,784
Expense Example, No Redemption, By Year, Column [Text] rr_ExpenseExampleNoRedemptionByYearColumnName Class A Shares
1 Year rr_ExpenseExampleNoRedemptionYear01 676
3 Years rr_ExpenseExampleNoRedemptionYear03 890
5 Years rr_ExpenseExampleNoRedemptionYear05 1,121
10 Years rr_ExpenseExampleNoRedemptionYear10 1,784
Perkins Mid Cap Value Fund | Class A, C, S, I, N, R, T Shares | Class C
  
Risk/Return: rr_RiskReturnAbstract  
Shareholder Fees Column [Text] rr_ShareholderFeesColumnName Class C
Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds) rr_MaximumDeferredSalesChargeOverOther 1.00%
Operating Expenses Column [Text] rr_OperatingExpensesColumnName Class C
Management Fees (may adjust up or down) rr_ManagementFeesOverAssets 0.54%
Distribution/Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 1.00%
Other Expenses rr_OtherExpensesOverAssets 0.24%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.78% [1]
Fee Waiver rr_FeeWaiverOrReimbursementOverAssets 0.02% [1]
Total Annual Fund Operating Expenses After Fee Waiver rr_NetExpensesOverAssets 1.76% [1]
Expense Example, By Year, Column [Text] rr_ExpenseExampleByYearColumnName Class C Shares
1 Year rr_ExpenseExampleYear01 281
3 Years rr_ExpenseExampleYear03 560
5 Years rr_ExpenseExampleYear05 964
10 Years rr_ExpenseExampleYear10 2,095
Expense Example, No Redemption, By Year, Column [Text] rr_ExpenseExampleNoRedemptionByYearColumnName Class C Shares
1 Year rr_ExpenseExampleNoRedemptionYear01 181
3 Years rr_ExpenseExampleNoRedemptionYear03 560
5 Years rr_ExpenseExampleNoRedemptionYear05 964
10 Years rr_ExpenseExampleNoRedemptionYear10 2,095
Perkins Mid Cap Value Fund | Class A, C, S, I, N, R, T Shares | Class S
  
Risk/Return: rr_RiskReturnAbstract  
Shareholder Fees Column [Text] rr_ShareholderFeesColumnName Class S
Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds) rr_MaximumDeferredSalesChargeOverOther none
Operating Expenses Column [Text] rr_OperatingExpensesColumnName Class S
Management Fees (may adjust up or down) rr_ManagementFeesOverAssets 0.54%
Distribution/Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses rr_OtherExpensesOverAssets 0.30%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.09% [1]
Fee Waiver rr_FeeWaiverOrReimbursementOverAssets none [1]
Total Annual Fund Operating Expenses After Fee Waiver rr_NetExpensesOverAssets 1.09% [1]
Expense Example, By Year, Column [Text] rr_ExpenseExampleByYearColumnName Class S Shares
1 Year rr_ExpenseExampleYear01 111
3 Years rr_ExpenseExampleYear03 347
5 Years rr_ExpenseExampleYear05 601
10 Years rr_ExpenseExampleYear10 1,329
Expense Example, No Redemption, By Year, Column [Text] rr_ExpenseExampleNoRedemptionByYearColumnName Class S Shares
1 Year rr_ExpenseExampleNoRedemptionYear01 111
3 Years rr_ExpenseExampleNoRedemptionYear03 347
5 Years rr_ExpenseExampleNoRedemptionYear05 601
10 Years rr_ExpenseExampleNoRedemptionYear10 1,329
Perkins Mid Cap Value Fund | Class A, C, S, I, N, R, T Shares | Class I
  
Risk/Return: rr_RiskReturnAbstract  
Shareholder Fees Column [Text] rr_ShareholderFeesColumnName Class I
Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds) rr_MaximumDeferredSalesChargeOverOther none
Operating Expenses Column [Text] rr_OperatingExpensesColumnName Class I
Management Fees (may adjust up or down) rr_ManagementFeesOverAssets 0.54%
Distribution/Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses rr_OtherExpensesOverAssets 0.19%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.73% [1]
Fee Waiver rr_FeeWaiverOrReimbursementOverAssets none [1]
Total Annual Fund Operating Expenses After Fee Waiver rr_NetExpensesOverAssets 0.73% [1]
Expense Example, By Year, Column [Text] rr_ExpenseExampleByYearColumnName Class I Shares
1 Year rr_ExpenseExampleYear01 75
3 Years rr_ExpenseExampleYear03 233
5 Years rr_ExpenseExampleYear05 406
10 Years rr_ExpenseExampleYear10 906
Expense Example, No Redemption, By Year, Column [Text] rr_ExpenseExampleNoRedemptionByYearColumnName Class I Shares
1 Year rr_ExpenseExampleNoRedemptionYear01 75
3 Years rr_ExpenseExampleNoRedemptionYear03 233
5 Years rr_ExpenseExampleNoRedemptionYear05 406
10 Years rr_ExpenseExampleNoRedemptionYear10 906
Perkins Mid Cap Value Fund | Class A, C, S, I, N, R, T Shares | Class N
  
Risk/Return: rr_RiskReturnAbstract  
Shareholder Fees Column [Text] rr_ShareholderFeesColumnName Class N
Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds) rr_MaximumDeferredSalesChargeOverOther none
Operating Expenses Column [Text] rr_OperatingExpensesColumnName Class N
Management Fees (may adjust up or down) rr_ManagementFeesOverAssets 0.54%
Distribution/Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses rr_OtherExpensesOverAssets 0.04% [2]
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.58% [1]
Fee Waiver rr_FeeWaiverOrReimbursementOverAssets none [1]
Total Annual Fund Operating Expenses After Fee Waiver rr_NetExpensesOverAssets 0.58% [1]
Expense Example, By Year, Column [Text] rr_ExpenseExampleByYearColumnName Class N Shares
1 Year rr_ExpenseExampleYear01 59
3 Years rr_ExpenseExampleYear03 186
5 Years rr_ExpenseExampleYear05 324
10 Years rr_ExpenseExampleYear10 726
Expense Example, No Redemption, By Year, Column [Text] rr_ExpenseExampleNoRedemptionByYearColumnName Class N Shares
1 Year rr_ExpenseExampleNoRedemptionYear01 59
3 Years rr_ExpenseExampleNoRedemptionYear03 186
5 Years rr_ExpenseExampleNoRedemptionYear05 324
10 Years rr_ExpenseExampleNoRedemptionYear10 726
Perkins Mid Cap Value Fund | Class A, C, S, I, N, R, T Shares | Class R
  
Risk/Return: rr_RiskReturnAbstract  
Shareholder Fees Column [Text] rr_ShareholderFeesColumnName Class R
Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds) rr_MaximumDeferredSalesChargeOverOther none
Operating Expenses Column [Text] rr_OperatingExpensesColumnName Class R
Management Fees (may adjust up or down) rr_ManagementFeesOverAssets 0.54%
Distribution/Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.50%
Other Expenses rr_OtherExpensesOverAssets 0.30%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.34% [1]
Fee Waiver rr_FeeWaiverOrReimbursementOverAssets none [1]
Total Annual Fund Operating Expenses After Fee Waiver rr_NetExpensesOverAssets 1.34% [1]
Expense Example, By Year, Column [Text] rr_ExpenseExampleByYearColumnName Class R Shares
1 Year rr_ExpenseExampleYear01 136
3 Years rr_ExpenseExampleYear03 425
5 Years rr_ExpenseExampleYear05 734
10 Years rr_ExpenseExampleYear10 1,613
Expense Example, No Redemption, By Year, Column [Text] rr_ExpenseExampleNoRedemptionByYearColumnName Class R Shares
1 Year rr_ExpenseExampleNoRedemptionYear01 136
3 Years rr_ExpenseExampleNoRedemptionYear03 425
5 Years rr_ExpenseExampleNoRedemptionYear05 734
10 Years rr_ExpenseExampleNoRedemptionYear10 1,613
Perkins Mid Cap Value Fund | Class A, C, S, I, N, R, T Shares | Class T
  
Risk/Return: rr_RiskReturnAbstract  
Shareholder Fees Column [Text] rr_ShareholderFeesColumnName Class T
Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds) rr_MaximumDeferredSalesChargeOverOther none
Operating Expenses Column [Text] rr_OperatingExpensesColumnName Class T
Management Fees (may adjust up or down) rr_ManagementFeesOverAssets 0.54%
Distribution/Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses rr_OtherExpensesOverAssets 0.30%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.84% [1]
Fee Waiver rr_FeeWaiverOrReimbursementOverAssets none [1]
Total Annual Fund Operating Expenses After Fee Waiver rr_NetExpensesOverAssets 0.84% [1]
Expense Example, By Year, Column [Text] rr_ExpenseExampleByYearColumnName Class T Shares
1 Year rr_ExpenseExampleYear01 86
3 Years rr_ExpenseExampleYear03 268
5 Years rr_ExpenseExampleYear05 466
10 Years rr_ExpenseExampleYear10 1,037
Expense Example, No Redemption, By Year, Column [Text] rr_ExpenseExampleNoRedemptionByYearColumnName Class T Shares
1 Year rr_ExpenseExampleNoRedemptionYear01 86
3 Years rr_ExpenseExampleNoRedemptionYear03 268
5 Years rr_ExpenseExampleNoRedemptionYear05 466
10 Years rr_ExpenseExampleNoRedemptionYear10 1,037
2002 rr_AnnualReturn2002 (13.09%)
2003 rr_AnnualReturn2003 39.33%
2004 rr_AnnualReturn2004 18.36%
2005 rr_AnnualReturn2005 10.36%
2006 rr_AnnualReturn2006 15.25%
2007 rr_AnnualReturn2007 7.43%
2008 rr_AnnualReturn2008 (27.33%)
2009 rr_AnnualReturn2009 30.37%
2010 rr_AnnualReturn2010 14.81%
2011 rr_AnnualReturn2011 (2.55%)
Bar Chart, Year to Date Return, Date rr_BarChartYearToDateReturnDate Sep. 30, 2012
Bar Chart, Year to Date Return rr_BarChartYearToDateReturn 9.06%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Best Quarter:
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2003
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 17.17%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Worst Quarter:
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2008
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (19.63%)
Perkins Mid Cap Value Fund | Class A, C, S, I, N, R, T Shares | Return Before Taxes | Class A
  
Risk/Return: rr_RiskReturnAbstract  
Column rr_AverageAnnualReturnColumnName Class A Shares
Label rr_AverageAnnualReturnLabel Return Before Taxes [3]
1 Year rr_AverageAnnualReturnYear01 (8.32%)
5 Years rr_AverageAnnualReturnYear05 1.24%
10 Years rr_AverageAnnualReturnYear10 6.75%
Since Inception of Predecessor Fund rr_AverageAnnualReturnSinceInception 11.12%
Inception Date rr_AverageAnnualReturnInceptionDate Aug. 12, 1998
Perkins Mid Cap Value Fund | Class A, C, S, I, N, R, T Shares | Return Before Taxes | Class C
  
Risk/Return: rr_RiskReturnAbstract  
Column rr_AverageAnnualReturnColumnName Class C Shares
Label rr_AverageAnnualReturnLabel Return Before Taxes [4]
1 Year rr_AverageAnnualReturnYear01 (4.27%)
5 Years rr_AverageAnnualReturnYear05 1.71%
10 Years rr_AverageAnnualReturnYear10 6.62%
Since Inception of Predecessor Fund rr_AverageAnnualReturnSinceInception 10.90%
Inception Date rr_AverageAnnualReturnInceptionDate Aug. 12, 1998
Perkins Mid Cap Value Fund | Class A, C, S, I, N, R, T Shares | Return Before Taxes | Class S
  
Risk/Return: rr_RiskReturnAbstract  
Column rr_AverageAnnualReturnColumnName Class S Shares
Label rr_AverageAnnualReturnLabel Return Before Taxes
1 Year rr_AverageAnnualReturnYear01 (2.73%)
5 Years rr_AverageAnnualReturnYear05 2.34%
10 Years rr_AverageAnnualReturnYear10 7.27%
Since Inception of Predecessor Fund rr_AverageAnnualReturnSinceInception 11.51%
Inception Date rr_AverageAnnualReturnInceptionDate Aug. 12, 1998
Perkins Mid Cap Value Fund | Class A, C, S, I, N, R, T Shares | Return Before Taxes | Class I
  
Risk/Return: rr_RiskReturnAbstract  
Column rr_AverageAnnualReturnColumnName Class I Shares
Label rr_AverageAnnualReturnLabel Return Before Taxes
1 Year rr_AverageAnnualReturnYear01 (2.43%)
5 Years rr_AverageAnnualReturnYear05 2.63%
10 Years rr_AverageAnnualReturnYear10 7.58%
Since Inception of Predecessor Fund rr_AverageAnnualReturnSinceInception 11.76%
Inception Date rr_AverageAnnualReturnInceptionDate Aug. 12, 1998
Perkins Mid Cap Value Fund | Class A, C, S, I, N, R, T Shares | Return Before Taxes | Class N
  
Risk/Return: rr_RiskReturnAbstract  
Column rr_AverageAnnualReturnColumnName Class N Shares
Label rr_AverageAnnualReturnLabel Return Before Taxes
1 Year rr_AverageAnnualReturnYear01 (2.55%)
5 Years rr_AverageAnnualReturnYear05 2.63%
10 Years rr_AverageAnnualReturnYear10 7.58%
Since Inception of Predecessor Fund rr_AverageAnnualReturnSinceInception 11.76%
Inception Date rr_AverageAnnualReturnInceptionDate Aug. 12, 1998
Perkins Mid Cap Value Fund | Class A, C, S, I, N, R, T Shares | Return Before Taxes | Class R
  
Risk/Return: rr_RiskReturnAbstract  
Column rr_AverageAnnualReturnColumnName Class R Shares
Label rr_AverageAnnualReturnLabel Return Before Taxes
1 Year rr_AverageAnnualReturnYear01 (3.01%)
5 Years rr_AverageAnnualReturnYear05 2.08%
10 Years rr_AverageAnnualReturnYear10 7.00%
Since Inception of Predecessor Fund rr_AverageAnnualReturnSinceInception 11.29%
Inception Date rr_AverageAnnualReturnInceptionDate Aug. 12, 1998
Perkins Mid Cap Value Fund | Class A, C, S, I, N, R, T Shares | Return Before Taxes | Class T
  
Risk/Return: rr_RiskReturnAbstract  
Column rr_AverageAnnualReturnColumnName Class T Shares
Label rr_AverageAnnualReturnLabel Return Before Taxes
1 Year rr_AverageAnnualReturnYear01 (2.55%)
5 Years rr_AverageAnnualReturnYear05 2.63%
10 Years rr_AverageAnnualReturnYear10 7.58%
Since Inception of Predecessor Fund rr_AverageAnnualReturnSinceInception 11.76%
Inception Date rr_AverageAnnualReturnInceptionDate Aug. 12, 1998
Perkins Mid Cap Value Fund | Class A, C, S, I, N, R, T Shares | Return After Taxes on Distributions | Class T
  
Risk/Return: rr_RiskReturnAbstract  
Column rr_AverageAnnualReturnColumnName Class T Shares
Label rr_AverageAnnualReturnLabel Return After Taxes on Distributions
1 Year rr_AverageAnnualReturnYear01 (3.88%)
5 Years rr_AverageAnnualReturnYear05 1.63%
10 Years rr_AverageAnnualReturnYear10 6.48%
Since Inception of Predecessor Fund rr_AverageAnnualReturnSinceInception 10.31%
Inception Date rr_AverageAnnualReturnInceptionDate Aug. 12, 1998
Perkins Mid Cap Value Fund | Class A, C, S, I, N, R, T Shares | Return After Taxes on Distributions and Sale of Fund Shares | Class T
  
Risk/Return: rr_RiskReturnAbstract  
Column rr_AverageAnnualReturnColumnName Class T Shares
Label rr_AverageAnnualReturnLabel Return After Taxes on Distributions and Sale of Fund Shares [5]
1 Year rr_AverageAnnualReturnYear01 (0.18%)
5 Years rr_AverageAnnualReturnYear05 2.04%
10 Years rr_AverageAnnualReturnYear10 6.34%
Since Inception of Predecessor Fund rr_AverageAnnualReturnSinceInception 9.94%
Inception Date rr_AverageAnnualReturnInceptionDate Aug. 12, 1998
Perkins Mid Cap Value Fund | Class A, C, S, I, N, R, T Shares | Russell Midcap Value Index (reflects no deduction for expenses, fees, or taxes)
  
Risk/Return: rr_RiskReturnAbstract  
Label rr_AverageAnnualReturnLabel Russell Midcap® Value Index
1 Year rr_AverageAnnualReturnYear01 (1.38%)
5 Years rr_AverageAnnualReturnYear05 0.04%
10 Years rr_AverageAnnualReturnYear10 7.67%
Since Inception of Predecessor Fund rr_AverageAnnualReturnSinceInception 7.70%
Inception Date rr_AverageAnnualReturnInceptionDate Aug. 12, 1998
[1] Janus Capital has contractually agreed to waive the Fund's total annual fund operating expenses (excluding any performance adjustments to management fees, the distribution and shareholder servicing fees - applicable to Class A Shares, Class C Shares, Class S Shares, and Class R Shares; administrative services fees payable pursuant to the Transfer Agency Agreement (except for networking and omnibus fees for Class A Shares, Class C Shares, and Class I Shares); brokerage commissions; interest; dividends; taxes; acquired fund fees and expenses; and extraordinary expenses) to 0.86% until at least November 1, 2013. The contractual waiver may be terminated or modified prior to this date only at the discretion of the Board of Trustees.
[2] Other Expenses for Class N Shares are based on the estimated expenses that the Shares expect to incur during their initial fiscal period.
[3] Calculated assuming maximum permitted sales loads.
[4] The one year return is calculated to include the contingent deferred sales charge.
[5] If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund's other return figures.