Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	FEDERATED ADJUSTABLE RATE SECURITIES FUND
Prospectus Date	rr_ProspectusDate	Oct. 31, 2012
FEDERATED ADJUSTABLE RATE SECURITIES FUND
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	Federated Adjustable Rate Securities Fund (the "Fund")
Objective [Heading]	rr_ObjectiveHeading	RISK/RETURN SUMMARY: INVESTMENT OBJECTIVE
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	The Fund's investment objective is to provide current income consistent with minimal volatility of principal.
Expense [Heading]	rr_ExpenseHeading	RISK/RETURN SUMMARY: FEES AND EXPENSES
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	This table describes the fees and expenses that you may pay if you buy and hold Institutional Shares (IS) or Service Shares (SS) of the Fund.
Shareholder Fees Caption [Text]	rr_ShareholderFeesCaption	Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text]	rr_OperatingExpensesCaption	Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination	rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination	November 1, 2013
Fee Waiver or Reimbursement Over Assets, Later of Termination Date or Next Effective Prospectus	farsf_FeeWaiverOrReimbursementOverAssetsLaterOfTerminationDateOrNextEffectiveProspectus	up to but not including the later of (the "Termination Date"): (a) November 1, 2013; or (b) the date of the Fund's next effective Prospectus.
Portfolio Turnover [Heading]	rr_PortfolioTurnoverHeading	Portfolio Turnover
Portfolio Turnover [Text Block]	rr_PortfolioTurnoverTextBlock	The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund Shares are held in a taxable account. These costs, which are not reflected in Annual Fund Operating Expenses or in the Example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 35% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	35.00%
Expense Example [Heading]	rr_ExpenseExampleHeading	Example
Expense Example Narrative [Text Block]	rr_ExpenseExampleNarrativeTextBlock	This Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 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 operating expenses are as shown in the table above and remain the same. Although your actual costs and returns may be higher or lower, based on these assumptions your costs would be:
Strategy [Heading]	rr_StrategyHeading	RISK/RETURN SUMMARY: INVESTMENTS, RISKS and PERFORMANCE What are the Fund's Main Investment Strategies?
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	The Fund is intended to provide investment income from securities paying interest at rates that increase or decrease in response to changes in market interest rates. The Fund's overall strategy is therefore to invest in a portfolio of adjustable-rate securities, including adjustable-rate, mortgage-backed securities (ARMs) and floating-rate, collateralized mortgage obligations (CMOs) issued or guaranteed by U.S. government agencies and government sponsored enterprises (GSEs). As a fundamental investment policy, the Fund invests at least 65% of the value of its total assets in a professionally managed portfolio of U.S. government securities consisting primarily of adjustable and floating rate mortgage securities which are issued or guaranteed by the U.S. government, its agencies or instrumentalities. The Fund may also invest in ARMs and floating-rate CMOs that are not issued or guaranteed by a GSE but that are rated by a nationally recognized statistical rating organization (NRSRO) in one of its two highest categories. Under normal circumstances, the Fund may also invest up to 20% of its assets in fixed-rate, mortgage-backed securities and other fixed-rate securities. The Fund's investment strategy will depend primarily on the types of ARMs and CMOs available in the market. Certain of the government securities in which the Fund invests are not backed by the full faith and credit of the U.S. government, such as those issued by the Federal Home Loan Mortgage Corporation ("Freddie Mac"), the Federal National Mortgage Association ("Fannie Mae") and the Federal Home Loan Bank System. These entities are, however, supported through federal subsidies, loans or other benefits. The Fund may also invest in government securities that are supported by the full faith and credit of the U.S. government, such as those issued by the Government National Mortgage Association ("Ginnie Mae"). Finally, the Fund may invest in a few government securities that have no explicit financial support, but which are regarded as having implied support because the federal government sponsors their activities. Because the Fund refers to adjustable rate investments in its name, it will notify shareholders at least 60 days in advance of any change in its investment policies that would enable the Fund to invest, under normal circumstances, less than 80 percent of its assets in adjustable rate securities. For purposes of this limitation, an adjustable rate security includes any fixed-income security that requires periodic changes in its interest rate based upon changes in a recognized index interest rate or another method of determining prevailing interest rates.
Risk [Heading]	rr_RiskHeading	What are the Main Risks of Investing in the Fund?
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	All mutual funds take investment risks. Therefore, it is possible to lose money by investing in the Fund. The primary factors that may reduce the Fund's returns include: Interest Rate Risk. Prices of fixed-income securities generally fall when interest rates rise. Interest rate changes have a greater effect on the price of fixed-income securities with longer durations. Duration measures the price sensitivity of a fixed-income security to changes in interest rates. Prepayment Risk. When homeowners prepay their mortgages in response to lower interest rates, the Fund will be required to reinvest the proceeds at the lower interest rates available. Also, when interest rates fall, the price of mortgage-backed securities may not rise to as great an extent as that of other fixed-income securities. Credit Risk. It is possible that interest or principal on securities will not be paid when due. Such non-payment or default may reduce the value of the Fund's portfolio holdings, its share price and its performance. Liquidity Risk. The non-government, mortgage-backed securities in which the Fund invests may be less readily marketable and may be subject to greater fluctuation in price than other securities. MBS Risk. A rise in interest rates may cause the value of MBS held by the Fund to decline. Certain MBS issued by GSEs are not backed by the full faith and credit of the U.S. government. A non-agency MBS is subject to the risk that the value of such security will decline, because the security is not issued or guaranteed as to principal or interest by the U.S. government or a GSE. The Fund's investments in collateralized mortgage obligations (CMOs) may entail greater market, prepayment and liquidity risks than other MBS. The Shares offered by this Prospectus are not deposits or obligations of any bank, are not endorsed or guaranteed by any bank and are not insured or guaranteed by the U.S. government, the Federal Deposit Insurance Corporation, the Federal Reserve Board or any other government agency.
Risk Lose Money [Text]	rr_RiskLoseMoney	All mutual funds take investment risks. Therefore, it is possible to lose money by investing in the Fund.
Risk Not Insured Depository Institution [Text]	rr_RiskNotInsuredDepositoryInstitution	The Shares offered by this Prospectus are not deposits or obligations of any bank, are not endorsed or guaranteed by any bank and are not insured or guaranteed by the U.S. government, the Federal Deposit Insurance Corporation, the Federal Reserve Board or any other government agency.
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	Performance: Bar Chart and Table Risk/Return Bar Chart
Performance Narrative [Text Block]	rr_PerformanceNarrativeTextBlock	The bar chart and performance table below reflect historical performance data for the Fund and are intended to help you analyze the Fund's investment risks in light of its historical returns. The bar chart shows the variability of the Fund's IS class total returns on a calendar year-by-year basis. The Average Annual Total Return Table shows returns averaged over the stated periods, and includes comparative performance information. The Fund's performance will fluctuate, and past performance (before and after taxes) is not necessarily an indication of future results. Updated performance information for the Fund is available under the "Products" section at FederatedInvestors.com or by calling 1-800-341-7400.
Performance Information Illustrates Variability of Returns [Text]	rr_PerformanceInformationIllustratesVariabilityOfReturns	The bar chart shows the variability of the Fund's IS class total returns on a calendar year-by-year basis.
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	1-800-341-7400
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	FederatedInvestors.com
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	The Fund's performance will fluctuate, and past performance (before and after taxes) is not necessarily an indication of future results.
Bar Chart [Heading]	rr_BarChartHeading	Federated Adjustable Rate Securities Fund - IS Class
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	The Fund's IS class total return for the nine-month period from January 1, 2012 to September 30, 2012, was 1.41%. Within the periods shown in the bar chart, the Fund's IS class highest quarterly return was 1.70% (quarter ended September 30, 2006). Its lowest quarterly return was (0.42)% (quarter ended June 30, 2004).
Performance Table Heading	rr_PerformanceTableHeading	Average Annual Total Return Table
Performance Table Uses Highest Federal Rate	rr_PerformanceTableUsesHighestFederalRate	After-tax returns are calculated using a standard set of assumptions. The stated returns assume the highest historical federal income and capital gains tax rates. These after-tax returns do not reflect the effect of any applicable state and local taxes.
Performance Table Not Relevant to Tax Deferred	rr_PerformanceTableNotRelevantToTaxDeferred	After-tax returns are not relevant to investors holding shares through a 401(k) plan, an Individual Retirement Account or other tax-advantaged investment plan.
Performance Table One Class of after Tax Shown [Text]	rr_PerformanceTableOneClassOfAfterTaxShown	After-tax returns are shown only for IS class, and after-tax returns for the SS class will differ from those shown for the IS class.
Performance Table Narrative	rr_PerformanceTableNarrativeTextBlock	In addition to Return Before Taxes, Return After Taxes is shown for the Fund's IS class to illustrate the effect of federal taxes on Fund returns. After-tax returns are shown only for IS class, and after-tax returns for the SS class will differ from those shown for the IS class. Actual after-tax returns depend on each investor's personal tax situation, and are likely to differ from those shown. After-tax returns are calculated using a standard set of assumptions. The stated returns assume the highest historical federal income and capital gains tax rates. These after-tax returns do not reflect the effect of any applicable state and local taxes. After-tax returns are not relevant to investors holding shares through a 401(k) plan, an Individual Retirement Account or other tax-advantaged investment plan. (For the Period Ended December 31, 2011)
FEDERATED ADJUSTABLE RATE SECURITIES FUND | IS
Risk/Return:	rr_RiskReturnAbstract
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, as applicable)	rr_MaximumDeferredSalesChargeOverOfferingPrice	none
Maximum Sales Charge (Load) Imposed on Reinvested Dividends (and other Distributions) (as a percentage of offering price)	rr_MaximumSalesChargeOnReinvestedDividendsAndDistributionsOverOther	none
Redemption Fee (as a percentage of amount redeemed, if applicable)	rr_RedemptionFeeOverRedemption	none
Exchange Fee	rr_ExchangeFeeOverRedemption	none
Management Fee	rr_ManagementFeesOverAssets	0.60%
Distribution (12b-1) Fee	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	0.40%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.00%
Fee Waivers and/or Expense Reimbursements	rr_FeeWaiverOrReimbursementOverAssets	0.36%	[1]
Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements	rr_NetExpensesOverAssets	0.64%
1 Year	rr_ExpenseExampleYear01	102
3 Years	rr_ExpenseExampleYear03	318
5 Years	rr_ExpenseExampleYear05	552
10 Years	rr_ExpenseExampleYear10	1,225
2002	rr_AnnualReturn2002	3.10%
2003	rr_AnnualReturn2003	1.61%
2004	rr_AnnualReturn2004	1.34%
2005	rr_AnnualReturn2005	2.39%
2006	rr_AnnualReturn2006	4.30%
2007	rr_AnnualReturn2007	5.50%
2008	rr_AnnualReturn2008	4.16%
2009	rr_AnnualReturn2009	4.17%
2010	rr_AnnualReturn2010	1.72%
2011	rr_AnnualReturn2011	1.16%
Year to Date Return, Label	rr_YearToDateReturnLabel	The Fund's IS class total return for the nine-month period
Bar Chart, Year to Date Return, Date	rr_BarChartYearToDateReturnDate	Sep. 30, 2012
Bar Chart, Year to Date Return	rr_BarChartYearToDateReturn	1.41%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	highest quarterly return
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Sep. 30, 2006
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	1.70%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	lowest quarterly return
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Jun. 30, 2004
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(0.42%)
1 Year	rr_AverageAnnualReturnYear01	1.16%
5 Years	rr_AverageAnnualReturnYear05	3.33%
10 Years	rr_AverageAnnualReturnYear10	2.93%
FEDERATED ADJUSTABLE RATE SECURITIES FUND | SS
Risk/Return:	rr_RiskReturnAbstract
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, as applicable)	rr_MaximumDeferredSalesChargeOverOfferingPrice	none
Maximum Sales Charge (Load) Imposed on Reinvested Dividends (and other Distributions) (as a percentage of offering price)	rr_MaximumSalesChargeOnReinvestedDividendsAndDistributionsOverOther	none
Redemption Fee (as a percentage of amount redeemed, if applicable)	rr_RedemptionFeeOverRedemption	none
Exchange Fee	rr_ExchangeFeeOverRedemption	none
Management Fee	rr_ManagementFeesOverAssets	0.60%
Distribution (12b-1) Fee	rr_DistributionAndService12b1FeesOverAssets	0.05%
Other Expenses	rr_OtherExpensesOverAssets	0.40%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.05%
Fee Waivers and/or Expense Reimbursements	rr_FeeWaiverOrReimbursementOverAssets	0.16%	[1]
Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements	rr_NetExpensesOverAssets	0.89%
1 Year	rr_ExpenseExampleYear01	107
3 Years	rr_ExpenseExampleYear03	334
5 Years	rr_ExpenseExampleYear05	579
10 Years	rr_ExpenseExampleYear10	1,283
1 Year	rr_AverageAnnualReturnYear01	0.91%
5 Years	rr_AverageAnnualReturnYear05	3.09%
10 Years	rr_AverageAnnualReturnYear10	2.69%
FEDERATED ADJUSTABLE RATE SECURITIES FUND | Return After Taxes on Distributions | IS
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	0.82%
5 Years	rr_AverageAnnualReturnYear05	2.40%
10 Years	rr_AverageAnnualReturnYear10	1.96%
FEDERATED ADJUSTABLE RATE SECURITIES FUND | Return After Taxes on Distributions and Sale of Fund Shares | IS
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	0.75%
5 Years	rr_AverageAnnualReturnYear05	2.30%
10 Years	rr_AverageAnnualReturnYear10	1.93%
FEDERATED ADJUSTABLE RATE SECURITIES FUND | BofA Merrill Lynch 1-Year U.S. Treasury Note Index (reflects no deduction for fees, expenses or taxes)
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	0.57%	[2]
5 Years	rr_AverageAnnualReturnYear05	2.55%	[2]
10 Years	rr_AverageAnnualReturnYear10	2.49%	[2]

[1] The Adviser and its affiliates have voluntarily agreed to waive their fees and/or reimburse expenses so that the total annual fund operating expenses (excluding Acquired Fund Fees and Expenses, if any) paid by the Fund's IS and SS classes (after the voluntary waivers and/or reimbursements) will not exceed 0.64% and 0.89% (the "Fee Limit"), respectively, up to but not including the later of (the "Termination Date"): (a) November 1, 2013; or (b) the date of the Fund's next effective Prospectus. While the Adviser and its affiliates currently do not anticipate terminating or increasing these arrangements prior to the Termination Date, these arrangements may only be terminated or the Fee Limit increased prior to the Termination Date with the agreement of the Fund's Board of Trustees.

[2] The BofA Merrill Lynch 1-Year U.S. Treasury Note Index is an unmanaged index tracking one-year U.S. government securities.