2.4.0.8000419 - Disclosure - Risk/Return Detail Data {Elements} - NORTHERN INVESTORS VARIABLE NAV AMT-FREE MUNICIPAL MONEY MARKET FUNDtruetruefalse1false falsefalseDuration_01Aug2012_31Jul2013http://www.sec.gov/CIK0000916620duration2012-08-01T00:00:002013-07-31T00:00:001true 2rr_RiskReturnAbstractrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Risk/Return:2false 3dei_EntityRegistrantNamedei_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00NORTHERN FUNDSfalsefalsefalsexbrli:normalizedStringItemTypenormalizedstringThe exact name of the entity filing the report as specified in its charter, which is required by forms filed with the SEC.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation 12B -Number 240 -Section 12b -Subsection 1 false0Registrant Name3false 3rr_ProspectusDaterr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse002013-07-31falsefalsetruexbrli:dateItemTypedateThe date of the prospectus.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 1 -Subsection a -Paragraph 3 false0Prospectus Date4false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse2false truefalseDuration_01Aug2012_31Jul2013S000029666_Memberhttp://www.sec.gov/CIK0000916620duration2012-08-01T00:00:002013-07-31T00:00:00falsefalseNORTHERN INVESTORS VARIABLE NAV AMT-FREE MUNICIPAL MONEY MARKET FUNDdei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldinf_S000029666Memberdei_LegalEntityAxisexplicitMembernanafalse0NORTHERN INVESTORS VARIABLE NAV AMT-FREE MUNICIPAL MONEY MARKET FUND5true 2rr_RiskReturnAbstractrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Risk/Return:6false 3rr_RiskReturnHeadingrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00<a name="tx553038_3"></a>INVESTORS VARIABLE NAV AMT-FREE MUNICIPAL MONEY MARKET FUND falsefalsefalsexbrli:stringItemTypestringRisk/Return Summary Investment Objectives/Goals Include the following information, in plain English under rule 421(d) under the Securities Act, in the order and subject matter indicatedReference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 2 false0Risk/Return [Heading]7false 3rr_ObjectiveHeadingrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00INVESTMENT OBJECTIVE falsefalsefalsexbrli:stringItemTypestringInvestment Objectives/Goals. Disclose the Fund's investment objectives or goals. A Fund also may identify its type or category (e.g., that it is a Money Market Fund or a balanced fund).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 2 -Subsection a false0Objective [Heading]8false 3rr_ObjectivePrimaryTextBlockrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00The Fund is a money market fund that seeks to provide, to the extent consistent with the preservation of capital and prescribed portfolio standards, a high level of income exempt from regular federal income tax by investing primarily in municipal instruments.falsefalsefalsenonnum:textBlockItemTypenaInvestment Objectives/Goals. Disclose the Fund's investment objectives or goals. A Fund also may identify its type or category (e.g., that it is a Money Market Fund or a balanced fund).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 2 -Subsection a false0Objective, Primary [Text Block]9false 3rr_ExpenseHeadingrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00FEES AND EXPENSES OF THE FUND falsefalsefalsexbrli:stringItemTypestringRisk/Return Summary Fee Table Includes the following information, in plain English under rule 421(d) under the Securities Act, after Item 2 Fees and expenses of the Fund This table describes the fees and expenses that you may pay if you buy and hold shared of the Fund. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $[_____] in [name of fund family] funds. Shareholder Fees (fees paid directly from your investment) Example 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 you redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return per year and that the Fund's operating expenses remained the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be You would pay the following expenses if you did not redeem your shares The Example does not reflect sales charges (loads) on reinvested dividends [and other distributions]. If these sales charges (loads) were included, your costs would be higher. Portfolio Turnover The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover may indicate higher transaction costs. 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 __% of the average value of its whole portfolio. Instructions. A.3.instructions.6 New Funds. For purposes of this Item, a "New Fund" is a Fund that does not include in Form N-1A financial statements reporting operating results or that includes financial statements for the Fund's initial fiscal year reporting operating results for a period of 6 months or less. The following Instructions apply to New Funds.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection instructions -Paragraph 1 -Subparagraph d false0Expense [Heading]10false 3rr_ExpenseNarrativeTextBlockrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.falsefalsefalsenonnum:textBlockItemTypenaThis table describes the fees and expenses that you may pay if you buy and hold shared of the Fund. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $[_____] in [name of fund family] funds. Include the narrative explanations in the order indicated. A Fund may modify the narrative explanations if the explanation contains comparable information to that shown. The narrative explanation regarding sales charge discounts is only required by a Fund that offers such discounts and should specify the minimum level of investment required to qualify for a discount. Modify the narrative explanation to state that Fund shares are sold on a national securities exchange at the end of the time periods indicated, and that brokerage commissions for buying and selling Fund shares through a broker are not reflected.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection instructions -Paragraph 1 -Subparagraph b false0Expense Narrative [Text Block]11false 3rr_ShareholderFeesCaptionrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00Shareholder Fees (fees paid directly from your investment)falsefalsefalsexbrli:stringItemTypestringShareholder Fees (fees paid directly from your investment).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection table -Paragraph 1 false0Shareholder Fees Caption [Text]12false 3rr_OperatingExpensesCaptionrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)falsefalsefalsexbrli:stringItemTypestringAnnual Fund Operating Expenses (ongoing expenses that you pay each year as a percentage of the value of your investment)Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection table -Paragraph 1 -Subparagraph 7 false0Operating Expenses Caption [Text]13false 3rr_FeeWaiverOrReimbursementOverAssetsDateOfTerminationrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00July 31, 2014falsefalsefalsexbrli:stringItemTypestringThis element represents the date of expected termination of any expense reimbursement or fee waiver arrangements that reduce any Fund operating expenses (SEC Form N-1A 2006-09-14 A.3.table.1.11 Total Annual Fund Operating Expenses A.3.instructions.3.e).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection instructions -Paragraph 3 -Subparagraph e false0Fee Waiver or Reimbursement over Assets, Date of Termination14false 3rr_OtherExpensesNewFundBasedOnEstimatesrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00"Other Expenses" are estimated for the current fiscal year since the Fund has not commenced operations as of the date of this Prospectus.falsefalsefalsexbrli:stringItemTypestringThis element represents the disclosure for new funds that "Other Expenses" are based on estimated amounts for the current fiscal year.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection instructions -Paragraph 6 -Subparagraph a false0Other Expenses, New Fund, Based on Estimates [Text]15false 3rr_ExpenseExampleHeadingrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00EXAMPLE falsefalsefalsexbrli:stringItemTypestringHeading for Expense Example.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection instructions -Paragraph 4 false0Expense Example [Heading]16false 3rr_ExpenseExampleNarrativeTextBlockrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00The following 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:falsefalsefalsenonnum:textBlockItemTypenaThe Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection example -Paragraph 1 -Subparagraph 1 false0Expense Example Narrative [Text Block]17false 3rr_StrategyHeadingrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00PRINCIPAL INVESTMENT STRATEGIES falsefalsefalsexbrli:stringItemTypestringPrincipal investment strategies of the Fund. Summarize how the Fund intends to achieve its investment objectives by identifying the Fund's principal investment strategies (including the type or types of securities in which the Fund invests or will invest principally) and any policy to concentrate in securities of issuers in a particular industry or group of industries.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection a false0Strategy [Heading]18false 3rr_StrategyNarrativeTextBlockrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00The Fund seeks to achieve its objective by investing primarily in high quality short-term municipal instruments, the interest on which is exempt from regular federal income tax. The high level of income sought by the Fund is relative to yields currently available in the tax-exempt marketplace. Municipal instruments may include, but are not limited to:<ul type="square"><li style="margin-left:-20px">Fixed, variable and floating rate notes and similar debt instruments;</li></ul><ul type="square"><li style="margin-left:-20px">Asset-backed securities that are considered municipal instruments (such as trust certificates backed by municipal bonds);</li></ul><ul type="square"><li style="margin-left:-20px">Tax-exempt commercial paper;</li></ul><ul type="square"><li style="margin-left:-20px">Municipal bonds, notes, paper or other instruments; and</li></ul><ul type="square"><li style="margin-left:-20px">Municipal bonds and notes that are guaranteed as principal and interest or backed by the U.S. government or by its agencies, instrumentalities or sponsored enterprises.</li></ul>Except in extraordinary circumstances, at least 80% of the Fund's net assets will be invested in debt instruments that pay interest that is exempt from regular federal income tax and alternative minimum tax. Under normal circumstances, it's the Fund's policy not to invest in alternative minimum tax ("AMT") obligations (also known as "private activity bonds"), using them only during temporary defensive periods or when non-AMT obligations are unavailable. AMT obligations pay interest that may be treated as an item of tax preference to shareholders under the federal AMT. To the extent that the Fund invests in AMT obligations, a portion of the Fund's dividends may be subject to federal income tax for shareholders subject to AMT. THE FUND HAS A VARIABLE NET ASSET VALUE ("NAV"). UNLIKE A TRADITIONAL MONEY MARKET FUND, THE FUND WILL NOT USE THE AMORTIZED COST METHOD OF VALUATION AND DOES NOT SEEK TO MAINTAIN A STABLE SHARE PRICE OF $1.00. AS A RESULT, THE FUND'S SHARE PRICE, WHICH IS ITS NAV, WILL VARY AND REFLECT THE EFFECTS OF UNREALIZED APPRECIATION AND DEPRECIATION AND REALIZED LOSSES AND GAINS. The Fund is managed in accordance with Rule 2a-7 ("Rule 2a-7") under the Investment Company Act of 1940, as amended (the "1940 Act"). Rule 2a-7 imposes strict requirements on the investment quality, maturity, and diversification of the Fund's investments. Accordingly, the Fund's investments must have a remaining maturity of no more than 397 days, and must be high quality. In addition, the Fund must maintain a dollar-weighted average maturity of 60 days or less, and a dollar-weighted average life of 120 days or less, without regard to interest rate resets. The Fund also maintains certain minimum standards regarding daily and weekly liquid assets, and limitations on the purchase of illiquid holdings, as required by Rule 2a-7. During extraordinary market conditions and interest rate environments, all or any portion of the Fund's assets may be uninvested or invested in taxable instruments. Uninvested assets do not generate income. The Fund may not achieve its investment objective during this time.falsefalsefalsenonnum:textBlockItemTypenaPrincipal investment strategies of the Fund. Summarize how the Fund intends to achieve its investment objectives by identifying the Fund's principal investment strategies (including the type or types of securities in which the Fund invests or will invest principally) and any policy to concentrate in securities of issuers in a particular industry or group of industries.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection a false0Strategy Narrative [Text Block]19false 3rr_RiskHeadingrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00PRINCIPAL RISKS falsefalsefalsexbrli:stringItemTypestringNarrative Risk Disclosure.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 1 false0Risk [Heading]20false 3rr_RiskNarrativeTextBlockrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00INTEREST RATE RISK is the risk that during periods of rising interest rates, the Fund's yield (and the market value of its securities) will tend to be lower than prevailing market rates; in periods of falling interest rates, the Fund's yield (and the market value of its securities) will tend to be higher. GUARANTOR (OR CREDIT ENHANCEMENT) RISK is the risk that changes in credit quality of a U.S. or foreign bank, insurance company or other financial institution or such entity's failure to fulfill its obligations could cause the Fund's investments to decline in value. Adverse developments in the banking or bond insurance industries also may negatively affect the Fund. PREPAYMENT (OR CALL) RISK is the risk that prepayment of the underlying mortgages or other collateral of some fixed-income securities may result in a decreased rate of return and a decline in value of those securities. DEBT EXTENSION RISK is the risk that an issuer will exercise its right to pay principal on an obligation held by the Fund (such as an asset-backed security) later than expected. This may happen during a period of rising interest rates. Under these circumstances, the value of the obligation will decrease and the Fund will suffer from the inability to invest in higher yielding securities. INCOME RISK is the risk that falling interest rates will cause the Fund's income to decline. Income risk is generally higher for short-term debt securities. MANAGEMENT RISK is the risk that a strategy used by the Fund's investment adviser may fail to produce the intended results. CREDIT (OR DEFAULT) RISK is the risk that the inability or unwillingness of an issuer or guarantor of a fixed-income security, or a counterparty to a repurchase or other transaction, to meet its payment or other financial obligations will adversely affect the value of the Fund's investments and its yield. Changes in the credit rating of a debt security held by the Fund could have a similar effect. PROJECT/INDUSTRIAL DEVELOPMENT BOND RISK is the risk that the Fund may be more sensitive to an adverse economic, business or political development if it invests more than 25% of its assets in municipal instruments, the interest upon which is paid solely from revenues of similar projects, or in industrial development bonds. TAX RISK is the risk that future legislative or administrative changes or court decisions may materially affect the value of municipal instruments or the ability of the Fund to pay tax-exempt dividends. MUNICIPAL MARKET VOLATILITY RISK is the risk that the Fund may be adversely affected by the volatile municipal market. The municipal market can be significantly affected by adverse tax, legislative, or political changes and the financial condition of the issuers of municipal securities. MARKET RISK is the risk that the market values of fixed-income securities owned by the Fund may decline, at times sharply and unpredictably. An investment in the Fund is not a deposit of any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation, any other government agency, or The Northern Trust Company, its affiliates, subsidiaries or any other bank. It is possible to lose money by investing in the Fund.falsefalsefalsenonnum:textBlockItemTypenaNarrative Risk Disclosure. A Fund may, in responding to this Item, describe the types of investors for whom the Fund is intended or the types of investment goals that may be consistent with an investment in the Fund.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 1 -Subparagraph i -Clause instruction false0Risk Narrative [Text Block]21false 3rr_RiskLoseMoneyrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00It is possible to lose money by investing in the Fund.falsefalsefalsexbrli:stringItemTypestringSummarize the principal risks of investing in the Fund, including the risks to which the Fund's portfolio as a whole is subject and the circumstances reasonably likely to affect adversely the Fund's net asset value, yield, and total return. Unless the Fund is a Money Market Fund, disclose that loss of money is a risk of investing in the Fund. A Fund may, in responding to this Item, describe the types of investors for whom the Fund is intended or the types of investment goals that may be consistent with an investment in the Fund.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 1 -Subparagraph i false0Risk Lose Money [Text]22false 3rr_RiskMoneyMarketFundrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00It is possible to lose money by investing in the Fund.falsefalsefalsexbrli:stringItemTypestringSummarize the principal risks of investing in the Fund, including the risks to which the Fund's portfolio as a whole is subject and the circumstances reasonably likely to affect adversely the Fund's net asset value, yield, and total return. Unless the Fund is a Money Market Fund, disclose that loss of money is a risk of investing in the Fund. A Fund may, in responding to this Item, describe the types of investors for whom the Fund is intended or the types of investment goals that may be consistent with an investment in the Fund. If the Fund is a Money Market Fund, state that An investment in the Fund is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. Although the Fund seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Fund. A Money Market Fund that is advised by or sold through an insured depository institution should combine the disclosure required by Items 2(c)(1)(ii) and (iii) in a single statement.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 1 -Subparagraph i false0Risk Money Market Fund [Text]23false 3rr_RiskNotInsuredDepositoryInstitutionrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00An investment in the Fund is not a deposit of any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation, any other government agency, or The Northern Trust Company, its affiliates, subsidiaries or any other bank.falsefalsefalsexbrli:stringItemTypestringIf the Fund is advised by or sold through an insured depository institution, state that An investment in the Fund is not a deposit of the bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. A Money Market Fund that is advised by or sold through an insured depository institution should combine the disclosure required by Items 2(c)(1)(ii) and (iii) in a single statement.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 1 -Subparagraph iii false0Risk Not Insured Depository Institution [Text]24false 3rr_BarChartAndPerformanceTableHeadingrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00FUND PERFORMANCE falsefalsefalsexbrli:stringItemTypestringRisk/Return Bar Chart and Table.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 false0Bar Chart and Performance Table [Heading]25false 3rr_PerformanceNarrativeTextBlockrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00The bar chart and performance table have been omitted because the Fund has been in operation for less than one calendar year.falsefalsefalsenonnum:textBlockItemTypenaRisk/Return Bar Chart and Table.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 false0Performance Narrative [Text Block]26false 3rr_PerformanceOneYearOrLessrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00The bar chart and performance table have been omitted because the Fund has been in operation for less than one calendar year.falsefalsefalsexbrli:stringItemTypestringFor a Fund that provides annual total returns for only one calendar year or for a Fund that does not include the bar chart because it does not have annual returns for a full calendar year, modify, as appropriate, the narrative explanation required by stating that the information gives some indication of the risks of an investment in the Fund by comparing the Fund's performance with a broad measure of market performance). Provide a brief explanation of how the information illustrates the variability of the Fund's returns (e.g., by stating that the information provides some indication of the risks of investing in the Fund by showing changes in the Fund's performance from year to year and by showing how the Fund's average annual returns for 1, 5, and 10 years compare with those of a broad measure of market performance). Provide a statement to the effect that the Fund's past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph i Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph instructions -Clause 1 -Exhibit b false0Performance One Year or Less [Text]27false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse3false USDtruefalse$Duration_01Aug2012_31Jul2013S000029666_MemberC000091144_Memberhttp://www.sec.gov/CIK0000916620duration2012-08-01T00:00:002013-07-31T00:00:00falsefalseNORTHERN INVESTORS VARIABLE NAV AMT-FREE MUNICIPAL MONEY MARKET FUNDdei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldinf_S000029666Memberdei_LegalEntityAxisexplicitMemberfalsefalseNORTHERN INVESTORS VARIABLE NAV AMT-FREE MUNICIPAL MONEY MARKET FUNDrr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldinf_C000091144Memberrr_ProspectusShareClassAxisexplicitMemberpureStandardhttp://www.xbrl.org/2003/instancepure0USDStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$nanafalse0NORTHERN INVESTORS VARIABLE NAV AMT-FREE MUNICIPAL MONEY MARKET FUND | NORTHERN INVESTORS VARIABLE NAV AMT-FREE MUNICIPAL MONEY MARKET FUND28true 2rr_RiskReturnAbstractrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Risk/Return:29false 3rr_ShareholderFeeOtherrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalseverboseLabel1truefalsetrue00USD$falsetruefalserr:NonNegativeMonetaryTypemonetaryOther ExpensesReference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection table -Paragraph 1 -Subparagraph 10 false2Shareholder Fees (fees paid directly from your investment)30false 3rr_ManagementFeesOverAssetsrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalseverboseLabel1truetruetrue0.00250.0025falsefalsefalserr:NonNegativePure4TypepureManagement Fees include investment advisory fees (including any fees based on the Fund's performance), any other management fees payable to the investment adviser or its affiliates, and administrative fees payable to the investment adviser or its affiliates that are not included as "Other Expenses."Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection instructions -Paragraph 3 -Subparagraph a false0Management Fees31false 3rr_OtherExpensesOverAssetsrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalseverboseLabel1truetruetrue0.00250.0025[1]falsefalsefalserr:NonNegativePure4Typepure"Other Expenses" include all expenses not otherwise disclosed in the table that are deducted from the Fund's assets or charged to all shareholder accounts. The amount of expenses deducted from the Fund's assets are the amounts shown as expenses in the Fund's statement of operations (including increases resulting from complying with paragraph 2(g) of rule 6-07 of Regulation S-X [17 CFR 210.6-07]). "Other Expenses" do not include extraordinary expenses as determined under generally accepted accounting principles (see Accounting Principles Board Opinion No. 30). If extraordinary expenses were incurred that materially affected the Fund's "Other Expenses," disclose in a footnote to the table what "Other Expenses" would have been had the extraordinary expenses been included.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection instructions -Paragraph 3 -Subparagraph c -Clause i false0Other Expenses32false 3rr_Component1OtherExpensesOverAssetsrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalseverboseLabel1truetruetrue0.0010.001falsefalsefalserr:NonNegativePure4TypepureThe Fund may subdivide this caption into no more than three subcaptions that identify the largest expense or expenses comprising "Other Expenses," but must include a total of all "Other Expenses." Alternatively, the Fund may include the components of "Other Expenses" in a parenthetical to the caption.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection instructions -Paragraph 3 -Subparagraph c -Clause iii false0Administration Fees33false 3rr_Component2OtherExpensesOverAssetsrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalseverboseLabel1truetruetrue0.0010.001falsefalsefalserr:NonNegativePure4TypepureThe Fund may subdivide this caption into no more than three subcaptions that identify the largest expense or expenses comprising "Other Expenses," but must include a total of all "Other Expenses." Alternatively, the Fund may include the components of "Other Expenses" in a parenthetical to the caption.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection table -Paragraph 1 -Subparagraph 10 false0Transfer Agency Fees34false 3rr_Component3OtherExpensesOverAssetsrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalseverboseLabel1truetruetrue0.00050.0005falsefalsefalserr:NonNegativePure4TypepureThe Fund may subdivide this caption into no more than three subcaptions that identify the largest expense or expenses comprising "Other Expenses," but must include a total of all "Other Expenses." Alternatively, the Fund may include the components of "Other Expenses" in a parenthetical to the caption.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection instructions -Paragraph 3 -Subparagraph c -Clause iii false0Other Operating Expenses35false 3rr_ExpensesOverAssetsrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalseverboseLabel1truetruetrue0.0050.005falsefalsefalserr:NonNegativePure4TypepureTotal Annual Fund Operating Expenses. If the Fund is a Feeder Fund, reflect the aggregate expenses of the Feeder Fund and the Master Fund in a single fee table using the captions provided. In a footnote to the fee table, state that the table and Example reflect the expenses of both the Feeder and Master Funds. If the prospectus offers more than one Class of a Multiple Class Fund or more than one Feeder Fund that invests in the same Master Fund, provide a separate response for each Class or Feeder Fund. Base the percentages of "Annual Fund Operating Expenses" on amounts incurred during the Fund's most recent fiscal year, but include in expenses amounts that would have been incurred absent expense reimbursement or fee waiver arrangements. If the Fund has changed its fiscal year and, as a result, the most recent fiscal year is less than three months, use the fiscal year prior to the most recent fiscal year as the basis for determining "Annual Fund Operating Expenses."Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection instructions -Paragraph 3 -Subparagraph d false0Total Annual Fund Operating Expenses36false 3rr_FeeWaiverOrReimbursementOverAssetsrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsetruenegatedTerseLabel1truetruetrue0.00150.0015[2]falsefalsefalserr:NonPositivePure4TypepureTotal Annual Fund Operating Expenses. If there were expense reimbursement or fee waiver arrangements that reduced any Fund operating expenses and will continue to reduce them for no less than one year from the effective date of the Fund's registration statement, a Fund may add two captions to the table one caption showing the amount of the expense reimbursement or fee waiver, and a second caption showing the Fund's net expenses after subtracting the fee reimbursement or expense waiver from the total fund operating expenses. The Fund should place these additional captions directly below the "Total Annual Fund Operating Expenses" caption of the table and should use appropriate descriptive captions, such as "Fee Waiver [and/or Expense Reimbursement]" and "Total Annual Fund Operating Expenses After Fee Waiver [and/or Expense Reimbursement]," respectively. If the Fund provides this disclosure, also disclose the period for which the expense reimbursement or fee waiver arrangement is expected to continue, and briefly describe who can terminate the arrangement and under what circumstances.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection table -Paragraph 1 -Subparagraph 11 false0Expense Reimbursement37false 3rr_NetExpensesOverAssetsrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalseverboseLabel1truetruetrue0.00350.0035falsefalsefalserr:NonNegativePure4TypepureTotal Annual Fund Operating Expenses.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection table -Paragraph 1 -Subparagraph 11 false0Total Annual Fund Operating Expenses After Expense Reimbursement38false 3rr_ExpenseExampleYear01rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalseverboseLabel1truefalsetrue3636USD$falsefalsefalserr:NonNegativeMonetaryTypemonetaryThe Example assumes that you invest $10,000 in the Fund for the time periods indicated and then you redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return per year and that the Fund's operating expenses remained the same. Although your actual costs may be higher or lower.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection instructions -Paragraph 4 false21 Year39false 3rr_ExpenseExampleYear03rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalseverboseLabel1truefalsetrue145145USD$falsetruefalserr:NonNegativeMonetaryTypemonetaryThe Example assumes that you invest $10,000 in the Fund for the time periods indicated and then you redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return per year and that the Fund's operating expenses remained the same. Although your actual costs may be higher or lower.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection example -Paragraph 1 -Subparagraph 2 false23 Years1"Other Expenses" are estimated for the current fiscal year since the Fund has not commenced operations as of the date of this Prospectus.2 Northern Trust Investments, Inc. has contractually agreed to reimburse a portion of the operating expenses of the Fund (other than acquired fund fees and expenses; a portion of the compensation paid to each Trustee who is not an officer, director or employee of Northern Trust Corporation or its subsidiaries; expenses related to third-party consultants engaged by the Board of Trustees of the Trust; membership dues paid to the Investment Company Institute and Mutual Fund Directors Forum; and extraordinary expenses and interest, if any) to the extent the "Total Annual Fund Operating Expenses" exceed 0.35%. This contractual limitation may not be terminated before July 31, 2014 without the approval of the Board of Trustees. Northern Trust Investments, Inc. serves as the investment adviser and administrator to the Fund. The Northern Trust Company, an affiliate of Northern Trust Investments, Inc., serves as transfer agent, custodian and sub-administrator to the Fund.falseRisk/Return Detail Data - NORTHERN INVESTORS VARIABLE NAV AMT-FREE MUNICIPAL MONEY MARKET FUND (USD $)NoRoundingUnKnownUnKnownUnKnowntruefalsefalseSheethttp://www.northernfunds.com/role/DisclosureRiskReturnDetailDataElementsNORTHERNINVESTORSVARIABLENAVAMT-FREEMUNICIPALMONEYMARKETFUND139