2.4.0.8000431 - Document - Risk/Return Summary {Unlabeled} - NORTHERN INVESTORS VARIABLE NAV TREASURY MONEY MARKET FUNDfalsefalsetrue1false falsefalseDuration_01Aug2012_31Jul2013S000039812_Memberhttp://www.sec.gov/CIK0000916620duration2012-08-01T00:00:002013-07-31T00:00:001false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00NORTHERN INVESTORS VARIABLE NAV TREASURY MONEY MARKET FUNDfalsefalsefalse1false truefalseDuration_01Aug2012_31Jul2013S000039812_Memberhttp://www.sec.gov/CIK0000916620duration2012-08-01T00:00:002013-07-31T00:00:00falsefalsenf_S000039812Memberdei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldinf_S000039812Memberdei_LegalEntityAxisexplicitMembernanafalse0NORTHERN INVESTORS VARIABLE NAV TREASURY MONEY MARKET FUND2false 3rr_RiskReturnHeadingrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00<b>INVESTORS VARIABLE NAV TREASURY MONEY MARKET FUND </b>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]3false 3rr_ObjectiveHeadingrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00<b>INVESTMENT OBJECTIVE </b>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]4false 3rr_ObjectivePrimaryTextBlockrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00The Fund is a money market fund that seeks to maximize current income to the extent consistent with the preservation of capital and maintenance of liquidity by investing primarily in U.S. Treasury securities, securities guaranteed as to principal and interest by the U.S. government, and related repurchase agreements.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]5false 3rr_ExpenseHeadingrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00<b>FEES AND EXPENSES OF THE FUND </b>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]6false 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]7false 3rr_ShareholderFeesCaptionrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00<b> Shareholder Fees (fees paid directly from your investment)</b>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]8false 3rr_ShareholderFeesTableTextBlockrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00<div style="display:none">~ http://www.northernfunds.com/role/ScheduleShareholderFeesNORTHERNINVESTORSVARIABLENAVTREASURYMONEYMARKETFUND column period compact * ~</div>falsefalse<div style="display:none">~ http://www.northernfunds.com/role/ScheduleShareholderFeesNORTHERNINVESTORSVARIABLENAVTREASURYMONEYMARKETFUND column period compact * ~</div>falsehttp://www.northernfunds.com/role/ScheduleShareholderFeesNORTHERNINVESTORSVARIABLENAVTREASURYMONEYMARKETFUND000432 - Schedule - Shareholder Fees {- NORTHERN INVESTORS VARIABLE NAV TREASURY MONEY MARKET FUND}truefalsefalse1falseColumnperiodPeriod*Columndei_LegalEntityAxisAxis*Columnrr_ProspectusShareClassAxisAxis*ColumnunitUnit*duration2012-08-01T00:00:002013-07-31T00:00:00falsefalseNORTHERN INVESTORS VARIABLE NAV TREASURY MONEY MARKET FUNDdei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldinf_S000039812Memberdei_LegalEntityAxisexplicitMemberfalsefalseNORTHERN INVESTORS VARIABLE NAV TREASURY MONEY MARKET FUNDrr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldinf_C000123414Memberrr_ProspectusShareClassAxisexplicitMemberNORTHERN INVESTORS VARIABLE NAV TREASURY MONEY MARKET FUNDNORTHERN INVESTORS VARIABLE NAV TREASURY MONEY MARKET FUNDUSDStandardhttp://www.xbrl.org/2003/iso4217USDiso42170 USDfalsefalseduration2012-08-01T00:00:002013-07-31T00:00:00$1falseRowprimaryElement*3false 3rr_ShareholderFeeOtherrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalseverboseLabelrr: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) 0rr_ShareholderFeeOtherrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalseverboseLabel1truefalsetrue00falsefalsefalserr: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)falseShareholder Fees (USD $)UnKnownUnKnownUnKnownUnKnownfalsefalsefalseSheet11001105ColumnperiodPeriod*Columndei_LegalEntityAxisAxis*Columnrr_ProspectusShareClassAxisAxis*ColumnunitUnit*RowprimaryElement*falsenonnum:textBlockItemTypenaContains a command for the SEC Viewer for the role corresponding to ShareholderFeesData.No definition available.false0Shareholder Fees [Table]9false 3rr_OperatingExpensesCaptionrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00<b>Annual Fund Operating Expenses (expenses that you pay each year as a <br/>percentage of the value of your investment)</b>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]10false 3rr_AnnualFundOperatingExpensesTableTextBlockrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00<div style="display:none">~ http://www.northernfunds.com/role/ScheduleAnnualFundOperatingExpensesNORTHERNINVESTORSVARIABLENAVTREASURYMONEYMARKETFUND column period compact * ~</div> falsefalse<div style="display:none">~ http://www.northernfunds.com/role/ScheduleAnnualFundOperatingExpensesNORTHERNINVESTORSVARIABLENAVTREASURYMONEYMARKETFUND column period compact * ~</div> falsehttp://www.northernfunds.com/role/ScheduleAnnualFundOperatingExpensesNORTHERNINVESTORSVARIABLENAVTREASURYMONEYMARKETFUND000433 - Schedule - Annual Fund Operating Expenses {- NORTHERN INVESTORS VARIABLE NAV TREASURY MONEY MARKET FUND}truefalsefalse1falseColumnperiodPeriod*Columndei_LegalEntityAxisAxis*Columnrr_ProspectusShareClassAxisAxis*ColumnunitUnit*duration2012-08-01T00:00:002013-07-31T00:00:00falsefalseNORTHERN INVESTORS VARIABLE NAV TREASURY MONEY MARKET FUNDdei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldinf_S000039812Memberdei_LegalEntityAxisexplicitMemberfalsefalseNORTHERN INVESTORS VARIABLE NAV TREASURY MONEY MARKET FUNDrr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldinf_C000123414Memberrr_ProspectusShareClassAxisexplicitMemberNORTHERN INVESTORS VARIABLE NAV TREASURY MONEY MARKET FUNDNORTHERN INVESTORS VARIABLE NAV TREASURY MONEY MARKET FUNDpureStandardhttp://www.xbrl.org/2003/instancepure0Standard0 USDfalsefalseduration2012-08-01T00:00:002013-07-31T00:00:00$1falseRowprimaryElement*3false 3rr_ManagementFeesOverAssetsrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalseverboseLabelrr: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 Fees 0rr_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 Fees2falseRowprimaryElement*4false 3rr_OtherExpensesOverAssetsrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalsetotalLabelrr: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 true0Other Expenses 0rr_OtherExpensesOverAssetsrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalsetotalLabel[1]1truetruetrue0.00250.0025falsefalsefalserr: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 true0Other Expenses3falseRowprimaryElement*5false 3rr_Component1OtherExpensesOverAssetsrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalseverboseLabelrr: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 Fees 0rr_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 Fees4falseRowprimaryElement*6false 3rr_Component2OtherExpensesOverAssetsrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalseverboseLabelrr: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 Fees 0rr_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 Fees5falseRowprimaryElement*7false 3rr_Component3OtherExpensesOverAssetsrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalseverboseLabelrr: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 Expenses 0rr_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 Expenses6falseRowprimaryElement*8false 3rr_ExpensesOverAssetsrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalsetotalLabelrr: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 true0Total Annual Fund Operating Expenses 0rr_ExpensesOverAssetsrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalsetotalLabel1truetruetrue0.0050.005falsefalsefalserr: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 true0Total Annual Fund Operating Expenses7falseRowprimaryElement*9false 3rr_FeeWaiverOrReimbursementOverAssetsrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsetruenegatedTerseLabelrr: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 Reimbursement 0rr_FeeWaiverOrReimbursementOverAssetsrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsetruenegatedTerseLabel[2]1truetruetrue0.00150.0015falsefalsefalserr: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 Reimbursement8falseRowprimaryElement*10false 3rr_NetExpensesOverAssetsrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalsetotalLabelrr: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 true0Total Annual Fund Operating Expenses After Expense Reimbursement 0rr_NetExpensesOverAssetsrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalsetotalLabel1truetruetrue0.00350.0035falsefalsefalserr: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 true0Total Annual Fund Operating Expenses After Expense Reimbursement1 "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.falseAnnual Fund Operating Expenses UnKnownUnKnownUnKnownUnKnownfalsefalsefalseSheet180718012ColumnperiodPeriod*Columndei_LegalEntityAxisAxis*Columnrr_ProspectusShareClassAxisAxis*ColumnunitUnit*RowprimaryElement*falsenonnum:textBlockItemTypenaContains a command for the SEC Viewer for the role corresponding to OperatingExpensesData.No definition available.false0Annual Fund Operating Expenses [Table]11false 3rr_ExpenseExampleHeadingrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00<b>EXAMPLE </b>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]12false 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&#8217;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]13false 3rr_ExpenseExampleWithRedemptionTableTextBlockrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00<div style="display:none">~ http://www.northernfunds.com/role/ScheduleExpenseExampleTransposedNORTHERNINVESTORSVARIABLENAVTREASURYMONEYMARKETFUND column period compact * ~</div>falsefalse<div style="display:none">~ http://www.northernfunds.com/role/ScheduleExpenseExampleTransposedNORTHERNINVESTORSVARIABLENAVTREASURYMONEYMARKETFUND column period compact * ~</div>truehttp://www.northernfunds.com/role/ScheduleExpenseExampleTransposedNORTHERNINVESTORSVARIABLENAVTREASURYMONEYMARKETFUND000434 - Schedule - Expense Example {Transposed} {- NORTHERN INVESTORS VARIABLE NAV TREASURY MONEY MARKET FUND}truefalsefalse1falseColumnprimaryElement*3false 3rr_ExpenseExampleYear01rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalseverboseLabelrr: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 Year USDfalsefalse$2falseColumnprimaryElement*4false 3rr_ExpenseExampleYear03rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalseverboseLabelrr: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 Years USDfalsefalse$1falseRowperiodPeriod*Rowdei_LegalEntityAxisAxis*Rowrr_ProspectusShareClassAxisAxis*RowunitUnit*duration2012-08-01T00:00:002013-07-31T00:00:00falsefalseNORTHERN INVESTORS VARIABLE NAV TREASURY MONEY MARKET FUNDdei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldinf_S000039812Memberdei_LegalEntityAxisexplicitMemberfalsefalseNORTHERN INVESTORS VARIABLE NAV TREASURY MONEY MARKET FUNDrr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldinf_C000123414Memberrr_ProspectusShareClassAxisexplicitMemberNORTHERN INVESTORS VARIABLE NAV TREASURY MONEY MARKET FUNDNORTHERN INVESTORS VARIABLE NAV TREASURY MONEY MARKET FUNDUSDStandardhttp://www.xbrl.org/2003/iso4217USDiso42170 0truefalsefalsefalsefalsefalsefalsefalsefalse1truefalsetrue3636falsefalsefalse2truefalsetrue145145falsefalsefalsenanafalse0NORTHERN INVESTORS VARIABLE NAV TREASURY MONEY MARKET FUNDfalseExpense Example (USD $)UnKnownUnKnownUnKnownUnKnownfalsefalsefalseSheet211021010ColumnprimaryElement*RowperiodPeriod*Rowdei_LegalEntityAxisAxis*Rowrr_ProspectusShareClassAxisAxis*RowunitUnit*falsenonnum:textBlockItemTypenaContains a command for the SEC Viewer for the role corresponding to ExpenseExample.No definition available.false0Expense Example, With Redemption [Table]14false 3rr_StrategyHeadingrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00<b>PRINCIPAL INVESTMENT STRATEGIES </b>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]15false 3rr_StrategyNarrativeTextBlockrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00The Fund seeks to achieve its objective by investing, under normal circumstances, its net assets exclusively in:<ul type="square"><li style="margin-left:-20px"> Short-term bills, notes and other obligations issued or guaranteed by the U.S. Treasury ("Treasury Obligations");</li></ul><ul type="square"><li style="margin-left:-20px"> Repurchase agreements with counterparties collateralized fully by Treasury Obligations; and</li></ul><ul type="square"><li style="margin-left:-20px"> Shares of other money market portfolios of regulated investment companies that i) limit investments to Treasury Obligations and related repurchase agreements, and ii) determine net asset values ("NAVs") based on Rule 2a-7 ("Rule 2a-7") under the Investment Company Act of 1940, as amended (the "1940 Act").</li></ul>THE FUND HAS A VARIABLE 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 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.<br/><br/>The Fund's investment adviser may consider, among other things, credit, interest rate and prepayment risks as well as general market conditions when deciding whether to buy or sell investments for the Fund.<br/><br/> During extraordinary market conditions and interest rate environments, all or any portion of the Fund's assets may be uninvested and will therefore 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]16false 3rr_RiskHeadingrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00<b>PRINCIPAL RISKS </b>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]17false 3rr_RiskNarrativeTextBlockrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00<b>INTEREST RATE RISK</b> 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.<br/><br/> <b>GUARANTOR (OR CREDIT ENHANCEMENT) RISK</b> 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.<br/><br/> <b>PREPAYMENT (OR CALL) RISK</b> 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. <br/><br/><b>DEBT EXTENSION RISK</b> 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.<br/><br/> <b>INCOME RISK </b>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.<br/><br/> <b>MANAGEMENT RISK</b> is the risk that a strategy used by the Fund's investment adviser may fail to produce the intended results.<br/><br/> <b>CREDIT (OR DEFAULT) RISK</b> 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.<br/><br/> <b>MARKET RISK</b> is the risk that the market values of fixed-income securities owned by the Fund may decline, at times sharply and unpredictably.<br/><br/> <b>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.</b>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]18false 3rr_BarChartAndPerformanceTableHeadingrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00<b>FUND PERFORMANCE </b>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]19false 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]falseRisk/Return Summary - NORTHERN INVESTORS VARIABLE NAV TREASURY MONEY MARKET FUND (NORTHERN INVESTORS VARIABLE NAV TREASURY MONEY MARKET FUND)UnKnownUnKnownUnKnownUnKnowntruefalsefalseSheethttp://www.northernfunds.com/role/DocumentRiskReturnSummaryUnlabeledNORTHERNINVESTORSVARIABLENAVTREASURYMONEYMARKETFUND119