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FlexShares iBoxx 5-Year Target Duration TIPS Index Fund  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading FlexShares® iBoxx® 5-Year Target Duration TIPS Index Fund
Objective [Heading] rr_ObjectiveHeading Investment Objective
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock
The Fund seeks to provide investment results that, before fees and expenses, correspond generally to the price and yield performance of the iBoxx 5-Year Target Duration TIPS Index (the “Underlying Index”).
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, hold and sell shares of the Fund. Under the Fund’s Investment Advisory Agreement, the Fund is responsible for the following expenses: interest expenses, brokerage commissions and other trading expenses, fees and expenses of the independent trustees and their independent legal counsel, taxes and other extraordinary costs such as litigation and other expenses not incurred in the ordinary course of business. You will also incur usual and customary brokerage commissions and fees to financial intermediaries when buying or selling shares of the Fund in the secondary market, which are not reflected in the example that follows:
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual Fund Operating Expenses (expenses that you pay eachyear as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination March 1, 2026
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. Portfolio turnover may vary from year to year, as well as within a year. During the most recent fiscal year, the Fund’s portfolio turnover rate was 42% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 42.00%
Expense Example [Heading] rr_ExpenseExampleHeading Example
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock
The following Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other funds. The Example assumes that you invest $10,000 in the Fund for the time periods indicated and then sell 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 (taking into account the expense reimbursement arrangement for one year). Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Strategy [Heading] rr_StrategyHeading Principal Investment Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock
The Underlying Index is designed to reflect the performance of a selection of inflation protected public obligations of the U.S. Treasury, commonly known as “TIPS,” with a targeted average modified adjusted duration, as defined by S&P Dow Jones Indices LLC as the Index Provider (“Index Provider” or “SPDJI”), of approximately five years. The Underlying Index includes publicly issued TIPS that have maturity dates of at least three years but not more than twenty years from an index rebalancing date. TIPS are securities issued by the U.S. Treasury that are designed to provide inflation protection to investors. TIPS’ principal and interest payments are linked to an official inflation measure (as measured by the Consumer Price Index for All Urban Consumers, or CPI-U) and the payments are supported by the full faith and credit of the United States. As of December 31, 2024, there were 24 TIPS in the Underlying Index. The components of the Underlying Index are weighted by the Index Provider to achieve the targeted average modified adjusted duration and its composition is rebalanced monthly. The Fund generally rebalances its portfolio in accordance with the Underlying Index.
NTI uses a “passive” or indexing approach to try to achieve the Fund’s investment objective. Unlike many investment companies, the Fund does not try to “beat” the index it tracks and does not seek temporary defensive positions when markets decline or appear overvalued. NTI generally intends to replicate the constituent securities of the Fund’s Underlying Index. “Replication” is an indexing strategy in which a fund invests in substantially all of the securities in its underlying index in approximately the same proportions as in the underlying index. NTI may use a “representative sampling” strategy in certain circumstances, such as when it may not be possible or practicable to fully implement a replication strategy. Representative sampling is investing in a representative sample of securities that collectively has an investment profile similar to the Underlying Index. When the Fund uses representative sampling, it may or may not hold all of the securities that are included in the Underlying Index.
Under normal circumstances, the Fund will invest at least 80% of its total assets (exclusive of collateral held from securities lending) in the securities of the Underlying Index. The Fund may also invest up to 20% of its assets in cash and cash equivalents, including shares of money market funds advised by NTI or its affiliates, futures contracts and options on futures contracts, to-be-announced (“TBA”) transactions, as well as securities not included in the Underlying Index, but which NTI believes will help the Fund track its Underlying Index.
The Underlying Index is sponsored by the Index Provider, an organization that is independent of the Fund and NTI. The Index Provider determines the composition and relative weightings of the securities in the Underlying Index and publishes information regarding the market value of the Underlying Index.
The Fund may lend securities representing up to one-third of the value of the Fund’s total assets (including the value of the collateral received).
Industry Concentration Policy. The Fund will concentrate its investments (i.e., hold 25% or more of its total assets) in a particular industry or group of industries to approximately the same extent that the Underlying Index is concentrated. For purposes of this limitation, securities of the U.S. government (including its agencies and instrumentalities) are not considered to be issued by members of any industry.
Strategy Portfolio Concentration [Text] rr_StrategyPortfolioConcentration Industry Concentration Policy. The Fund will concentrate its investments (i.e., hold 25% or more of its total assets) in a particular industry or group of industries to approximately the same extent that the Underlying Index is concentrated. For purposes of this limitation, securities of the U.S. government (including its agencies and instrumentalities) are not considered to be issued by members of any industry.
Risk [Heading] rr_RiskHeading Principal Risks
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Fund Performance
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock
The bar chart and table that follow show how the Fund has performed on a calendar year basis and provide an indication of the risks of investing in the Fund by showing (A) changes in the Fund’s performance from year to year and (B) how the Fund’s average annual returns compare with those of a broad measure of market performance. Past performance (before and after taxes) does not necessarily indicate how the Fund will perform in the future. Updated information on the Fund’s performance results can be obtained by visiting flexshares.com.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The bar chart and table that follow show how the Fund has performed on a calendar year basis and provide an indication of the risks of investing in the Fund by showing (A) changes in the Fund’s performance from year to year and (B) how the Fund’s average annual returns compare with those of a broad measure of market performance.
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress flexshares.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Past performance (before and after taxes) does not necessarily indicate how the Fund will perform in the future.
Bar Chart [Heading] rr_BarChartHeading Calendar Year Total Returns
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock
For the periods shown in the bar chart above:
Best Quarter (12/31/2023): 4.53%
Worst Quarter (6/30/2022): -4.68%
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns (for the periods ended December 31, 2024) 
Performance Table Market Index Changed rr_PerformanceTableMarketIndexChanged In connection with new regulatory requirements, the Fund has changed its broad-based securities market benchmark from the iBoxx 5-Year Target Duration TIPS Index to the Bloomberg U.S. Aggregate Bond Index. The Fund will continue to compare its performance to the iBoxx 5-Year Target Duration TIPS Index, which reflects the market segments in which the Fund invests.
Index No Deduction for Fees, Expenses, Taxes [Text] rr_IndexNoDeductionForFeesExpensesTaxes Reflects no deduction for fees, expenses or taxes.
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred After-tax returns shown are not relevant to investors who hold shares through tax-advantaged arrangements, such as 401(k) plans or individual retirement plans.
Performance Table Explanation after Tax Higher rr_PerformanceTableExplanationAfterTaxHigher After-tax returns may exceed the return before taxes due to an assumed tax benefit from realizing a capital loss on a sale of Fund shares.
Performance Table Narrative rr_PerformanceTableNarrativeTextBlock
After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on an investor’s tax situation and may differ from those shown. After-tax returns shown are not relevant to investors who hold shares through tax-advantaged arrangements, such as 401(k) plans or individual retirement plans. After-tax returns may exceed the return before taxes due to an assumed tax benefit from realizing a capital loss on a sale of Fund shares.
FlexShares iBoxx 5-Year Target Duration TIPS Index Fund | Risk Lose Money [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock It is possible to lose money on an investment in the Fund.
FlexShares iBoxx 5-Year Target Duration TIPS Index Fund | Risk Not Insured Depository Institution [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock 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.
FlexShares iBoxx 5-Year Target Duration TIPS Index Fund | Inflation Protected Security Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
Inflation Protected Security Risk is the risk that the value of inflation protected securities, such as TIPS, generally will fluctuate in response to changes in real interest rates, generally decreasing when real interest rates rise and increasing when real interest rates fall. In addition, interest payments on inflation-protected securities will generally vary up or down along with the rate of inflation. Real interest rates are generally measured as a nominal interest less an inflation rate. As such, investors should be aware that an investment in TIPS over a particular timeframe may decrease in value even in an inflationary environment. There can be no assurance that the inflation index used will accurately measure the real rate of inflation in the prices of goods and services. Because of their inflation adjustment feature, inflation-protected bonds typically have lower yields than conventional fixed-rate bonds. In addition, the market for inflation-indexed securities may be less developed or liquid, and more volatile, than certain other securities markets. In addition, positive adjustments to principal generally will result in taxable income to the Fund at the time of such adjustments (which generally would be distributed by the Fund as part of its taxable dividends), even though the principal amount is not paid until maturity.
FlexShares iBoxx 5-Year Target Duration TIPS Index Fund | Income Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
Income Risk is the risk that the Fund's income may decline due to a decline in inflation (or deflation) or due to changes in inflation expectations.
FlexShares iBoxx 5-Year Target Duration TIPS Index Fund | Interest Rate Maturity Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
Interest Rate/Maturity Risk is the risk that the value of the Fund’s fixed-income assets will decline because of rising interest rates. In general, securities with longer maturities or durations are more sensitive to interest rate changes. Changing interest rates, including rates that fall below zero,
may have unpredictable effects on the markets and the Fund’s investments, may result in heightened market volatility, may impact the liquidity of fixed-income securities and of the Fund, and may detract from Fund performance. A low or negative interest rate environment could cause the Fund’s earnings to fall below the Fund’s expense ratio, resulting in a negative yield and a decline in the Fund’s share price. An increase in interest rates may cause investors to move out of fixed incomes securities on a large scale, which could adversely affect the price of fixed income securities, lead to heightened volatility in the fixed-income markets and may adversely affect the liquidity of certain fixed-income investments.
FlexShares iBoxx 5-Year Target Duration TIPS Index Fund | Market Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
Market Risk is the risk that the value of the Fund’s investments may increase or decrease in response to expected, real or perceived economic, political or financial events in the U.S. or global markets. The frequency and magnitude of such changes in value cannot be predicted. Certain securities and other investments held by the Fund may experience increased volatility, illiquidity, or other potentially adverse effects in response to changing market conditions, inflation, changes in interest rates, lack of liquidity in the bond or equity markets, or volatility in the equity markets. Market disruptions caused by local or regional events such as financial institution failure, war, acts of terrorism, the spread of infectious illness (including epidemics and pandemics) or other public health issues, recessions or other events or adverse investor sentiment could have a significant impact on the Fund and its investments. Such events could result in the Fund’s shares trading at increased premiums or discounts to the Fund’s NAV. During periods of market disruption or other abnormal market conditions, the Fund’s exposure to the risks described elsewhere in this summary will likely increase.
FlexShares iBoxx 5-Year Target Duration TIPS Index Fund | Index Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
Index Risk is the risk that the Fund would not necessarily buy or sell a security unless that security is added to or removed from, respectively, the Underlying Index, even if that security generally is underperforming, because unlike many investment companies, the Fund does not utilize an investing strategy that seeks returns in excess of the Underlying Index. Additionally, the Fund rebalances and/or reconstitutes its portfolio in accordance with the Underlying Index, and, therefore, any changes to the Underlying Index’s rebalance and/or reconstitution schedule will result in corresponding changes to the Fund’s rebalance and/or reconstitution schedule.
FlexShares iBoxx 5-Year Target Duration TIPS Index Fund | Tracking Error Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
Tracking Error Risk is the risk that the Fund’s performance may vary from the performance of the Underlying Index as a result of creation and redemption activity, transaction costs, expenses and other factors. Market disruptions, regulatory restrictions or other abnormal market conditions could have an adverse effect on the Fund's ability to adjust its exposure to required levels in order to track its Index or cause delays in the Underlying Index's rebalancing schedule. During any such delay, it is possible that the Underlying Index, and, in turn, the Fund will deviate from the Underlying Index's stated methodology and therefore experience returns different than those that would have been achieved under a normal rebalancing or reconstitution schedule.
FlexShares iBoxx 5-Year Target Duration TIPS Index Fund | Authorized Participant Concentration Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
Authorized Participant Concentration Risk is the risk that the Fund may be adversely affected because it has a limited number of institutions that act as authorized participants (“Authorized Participants”). Only an Authorized Participant may engage in creation or redemption transactions directly with the Fund and none of those Authorized Participants is obligated to engage in creation and/or redemption transactions. To the extent that these institutions exit the business or are unable or unwilling to proceed with creation and/or redemption orders with respect to the Fund and no other Authorized Participant is able or willing to step forward to create or redeem Creation Units (as defined below), Fund shares may trade at a discount to NAV and possibly face trading halts and/or delisting.
FlexShares iBoxx 5-Year Target Duration TIPS Index Fund | Concentration Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
Concentration Risk is the risk that, if the Fund is concentrated in a particular industry or group of industries, the Fund is likely to present more risks than a fund that is broadly diversified over several industries or groups of industries. Compared to the broad market, an individual industry may be more strongly affected by changes in the economic climate, broad market shifts, moves in a particular dominant stock or regulatory changes.
FlexShares iBoxx 5-Year Target Duration TIPS Index Fund | Calculation Methodology Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
Calculation Methodology Risk is the risk that the Underlying Index’s calculation methodology or sources of information may not provide an accurate assessment of included issuers or correct valuation of securities, nor is the availability or timeliness of the production of the Underlying Index guaranteed. A security included in the Underlying Index may not exhibit the characteristic or provide the specific exposure for which it was selected and consequently a Fund's holdings may not exhibit returns consistent with that characteristic or exposure.
FlexShares iBoxx 5-Year Target Duration TIPS Index Fund | Market Trading Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
Market Trading Risk is the risk that the Fund faces because its shares are listed on a securities exchange, including the potential lack of an active market for Fund shares, losses from trading in secondary markets, periods of high volatility and disruption in the creation/redemption process of the Fund. ANY OF THESE FACTORS MAY LEAD TO THE FUND’S SHARES TRADING AT A PREMIUM OR DISCOUNT TO NAV.
Trading in Fund shares may be halted due to market conditions or for reasons that, in the view of its listing exchange, make trading in the shares inadvisable. The market prices of Fund shares will generally fluctuate in accordance with changes in its NAV, changes in the relative supply of, and demand for, Fund shares, and changes in the liquidity, or the perceived liquidity, of the Fund’s holdings.
FlexShares iBoxx 5-Year Target Duration TIPS Index Fund | Derivatives Risks [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
Derivatives Risk is the risk that derivatives may pose risks in addition to and greater than those associated with investing directly in securities, currencies and other instruments, may be illiquid or less liquid, more volatile, more difficult to value and leveraged so that small changes in the value of the underlying instrument may produce disproportionate losses to the Fund. Derivatives are also subject to counterparty risk, which is the risk that the other party to the transaction will not perform its contractual obligations. The use of derivatives is a highly specialized activity that involves investment techniques and risks different from those associated with investments in more traditional securities and instruments.
•Futures Contracts Risk is the risk that there will be imperfect correlation between the change in market value of the Fund’s securities and the price of futures contracts, which may result in the strategy not working as intended; the possible inability of the Fund to sell or close out a futures contract at the desired time or price; losses due to unanticipated market movements, which potentially are unlimited; and the possible inability of NTI to correctly predict the direction of securities’ prices, interest rates, currency exchange rates and other economic factors, which may make the Fund’s returns more volatile or increase the risk of loss.•Options Contracts Risk Options contracts give the holder of the option the right to buy (or to sell) a position in a security or in a contract to the writer of the option, at a certain price. They are subject to correlation risk because there may be an imperfect correlation
between the options and the securities markets that cause a given transaction to fail to achieve its objectives. The successful use of options depends on the investment adviser’s ability to predict correctly future price fluctuations and the degree of correlation between the options and securities markets. Exchanges can limit the number of positions that can be held or controlled by the Fund or the investment adviser, thus limiting the ability to implement the Fund’s strategies.
FlexShares iBoxx 5-Year Target Duration TIPS Index Fund | TBA Transactions Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
TBA Transactions Risk is the risk of loss if the securities received are less favorable than what was anticipated by the Fund when entering into the TBA transaction. TBA transactions also involve the risk that the counterparty will fail to deliver the securities, exposing the Fund to further losses. Default or bankruptcy of a counterparty to a TBA transaction would expose the Fund to possible losses because of adverse market action, expenses or delays in connection with the purchase or sale of the pools of mortgage pass-through securities specified in the TBA transaction. Whether or not the Fund takes delivery of the securities at the termination date of a TBA transaction, the Fund will nonetheless be exposed to changes in the value of the underlying investments during the term of the agreement.
FlexShares iBoxx 5-Year Target Duration TIPS Index Fund | Credit or Default Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
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 TBA, repurchase or other transaction, to meet its payment or other financial obligations will adversely affect the value of the Fund’s investments and its returns. The credit quality of a debt security or of the issuer of a debt security held by the Fund could deteriorate rapidly, which may impair the Fund’s liquidity or cause a deterioration in the Fund’s NAV. The Fund could also be delayed or hindered in its enforcement of rights against an issuer, guarantor or counterparty. The degree of credit risk depends on the issuer’s or counterparty’s financial condition and on the terms of the securities.
FlexShares iBoxx 5-Year Target Duration TIPS Index Fund | Prepayment or Call Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
Prepayment (or Call) Risk is the risk that an issuer could exercise its right to pay principal on callable debt securities held by the Fund earlier than expected. Issuers may be more likely to prepay when interest rates fall, when credit spreads change, or when an issuer’s credit quality improves. If this happens, the Fund will not benefit from the rise in the market price of the securities that normally accompanies a decline in interest rates, and will be forced to reinvest prepayment proceeds in lower yielding securities, which may reduce the Fund’s returns. The Fund may also lose any premium it paid to purchase the securities.
FlexShares iBoxx 5-Year Target Duration TIPS Index Fund | Securities Lending Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
Securities Lending Risk is the risk that the Fund may lose money because the borrower of the loaned securities fails to return the securities in a timely manner or at all. The Fund could also lose money in the event of a decline in the value of collateral provided for loaned securities or a decline in the value of any investments made with cash collateral.
FlexShares iBoxx 5-Year Target Duration TIPS Index Fund | FlexShares iBoxx 5-Year Target Duration TIPS Index Fund  
Risk/Return: rr_RiskReturnAbstract  
Management Fees rr_ManagementFeesOverAssets 0.18%
Distribution (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses rr_OtherExpensesOverAssets 0.01%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.19%
Expense Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.01%) [1]
Total Annual Fund Operating Expenses After Expense Reimbursement rr_NetExpensesOverAssets 0.18%
1 Year rr_ExpenseExampleYear01 $ 18
3 Years rr_ExpenseExampleYear03 60
5 Years rr_ExpenseExampleYear05 106
10 Years rr_ExpenseExampleYear10 $ 242
2015 rr_AnnualReturn2015 (0.16%)
2016 rr_AnnualReturn2016 4.22%
2017 rr_AnnualReturn2017 1.97%
2018 rr_AnnualReturn2018 (0.86%)
2019 rr_AnnualReturn2019 7.96%
2020 rr_AnnualReturn2020 10.17%
2021 rr_AnnualReturn2021 5.29%
2022 rr_AnnualReturn2022 (9.47%)
2023 rr_AnnualReturn2023 4.19%
2024 rr_AnnualReturn2024 2.19%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Best Quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Dec. 31, 2023
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 4.53%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Worst Quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Jun. 30, 2022
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (4.68%)
One Year rr_AverageAnnualReturnYear01 2.19%
Five Year rr_AverageAnnualReturnYear05 2.26%
Ten Year rr_AverageAnnualReturnYear10 2.42%
FlexShares iBoxx 5-Year Target Duration TIPS Index Fund | After Taxes on Distributions | FlexShares iBoxx 5-Year Target Duration TIPS Index Fund  
Risk/Return: rr_RiskReturnAbstract  
One Year rr_AverageAnnualReturnYear01 0.55%
Five Year rr_AverageAnnualReturnYear05 0.56%
Ten Year rr_AverageAnnualReturnYear10 1.22%
FlexShares iBoxx 5-Year Target Duration TIPS Index Fund | After Taxes on Distributions and Sale of Shares | FlexShares iBoxx 5-Year Target Duration TIPS Index Fund  
Risk/Return: rr_RiskReturnAbstract  
One Year rr_AverageAnnualReturnYear01 1.28%
Five Year rr_AverageAnnualReturnYear05 1.02%
Ten Year rr_AverageAnnualReturnYear10 1.35%
FlexShares iBoxx 5-Year Target Duration TIPS Index Fund | Bloomberg U.S. Aggregate Bond Index  
Risk/Return: rr_RiskReturnAbstract  
One Year rr_AverageAnnualReturnYear01 1.25% [2],[3]
Five Year rr_AverageAnnualReturnYear05 (0.33%) [2],[3]
Ten Year rr_AverageAnnualReturnYear10 1.35% [2],[3]
FlexShares iBoxx 5-Year Target Duration TIPS Index Fund | iBoxx 5-Year Target Duration TIPS Index  
Risk/Return: rr_RiskReturnAbstract  
One Year rr_AverageAnnualReturnYear01 2.45% [3]
Five Year rr_AverageAnnualReturnYear05 2.48% [3]
Ten Year rr_AverageAnnualReturnYear10 2.56% [3]
[1] Northern Trust Investments, Inc. (“NTI”) has contractually agreed to reimburse a portion of the operating expenses of the Fund (other than 12b-1 Fees, Tax Expenses, Extraordinary Expenses, and Acquired Fund Fees and Expenses) to the extent the “Total Annual Fund Operating Expenses” exceed 0.18%. This contractual limitation may not be terminated before March 1, 2026 without the approval of the Fund’s Board of Trustees. The Fund’s Board of Trustees may terminate the contractual agreement at any time if it determines that it is in the best interest of the Fund and its shareholders.
[2] In connection with new regulatory requirements, the Fund has changed its broad-based securities market benchmark from the iBoxx 5-Year Target Duration TIPS Index to the Bloomberg U.S. Aggregate Bond Index. The Fund will continue to compare its performance to the iBoxx 5-Year Target Duration TIPS Index, which reflects the market segments in which the Fund invests.
[3] Reflects no deduction for fees, expenses or taxes.