Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	AMG Funds IV
Prospectus Date	rr_ProspectusDate	Mar. 01, 2019
AMG River Road Long-Short Fund
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	<b>AMG River Road Long-Short Fund</b>
Objective [Heading]	rr_ObjectiveHeading	<b>INVESTMENT OBJECTIVE</b>
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	The Fund seeks to provide absolute return while minimizing volatility over a full market cycle.
Expense [Heading]	rr_ExpenseHeading	<b>FEES AND EXPENSES OF THE FUND</b>
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	The table below describes the fees and expenses that you may pay if you buy and hold shares of the Fund. If you transact in Class I shares of the Fund through a financial intermediary, you may be required to pay a commission to the financial intermediary for effecting such transactions. Such commissions are charged by the financial intermediary and are not reflected in the table or Expense Example below.
Operating Expenses Caption [Text]	rr_OperatingExpensesCaption	Annual Fund Operating Expenses<br/>(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	March 1, 2020
Portfolio Turnover [Heading]	rr_PortfolioTurnoverHeading	<b>PORTFOLIO TURNOVER</b>
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 189% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	189.00%
Expenses Restated to Reflect Current [Text]	rr_ExpensesRestatedToReflectCurrent	Expense information has been restated to reflect current fees.
Expenses Not Correlated to Ratio Due to Acquired Fund Fees [Text]	rr_ExpensesNotCorrelatedToRatioDueToAcquiredFundFees	The Total Annual Fund Operating Expenses and Total Annual Fund Operating Expenses After Fee Waiver and Expense Reimbursements do not correlate to the ratios of expenses to average net assets in the Financial Highlights section of this Prospectus, which reflect only the operating expenses of the Fund and do not include fees and expenses of any acquired fund.
Expense Example [Heading]	rr_ExpenseExampleHeading	<b>EXPENSE EXAMPLE</b>
Expense Example Narrative [Text Block]	rr_ExpenseExampleNarrativeTextBlock	This Example will help you compare the cost of investing in the Fund to the cost of investing in other mutual funds. The Example makes certain assumptions. It assumes that you invest $10,000 as an initial investment in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. It also assumes that your investment has a 5% total return each year and the Fund’s operating expenses remain the same. The Example includes the Fund’s contractual expense limitation through March 1, 2020. Although your actual costs may be higher or lower, based on the above assumptions, your costs would be:
Strategy [Heading]	rr_StrategyHeading	<b>PRINCIPAL INVESTMENT STRATEGIES</b>
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	The Fund pursues its investment objective primarily by taking long and short positions in equity securities. River Road Asset Management, LLC, the subadviser to the Fund (“River Road” or the “Subadviser”), believes that a combination of long and short positions may provide positive returns through a complete market cycle and may offer reduced risk. The allocation between long and short positions is a result of the Subadviser’s fundamental investment process. The Fund does not intend to be market neutral and anticipates that it will normally hold a higher percentage of its assets in long positions (i.e., the Fund will be “net long”). The Fund’s long and short equity investments consist primarily of domestic common stock and real estate investment trusts (“REITs”) but may also include other types of equity securities such as foreign stock, preferred stock, convertible preferred stocks, publicly traded partnerships (“PTPs”) and convertible bonds. The Fund may use instruments such as exchange-traded funds (“ETFs”), options, futures and other index-based investments to manage its exposure between long and short positions. The use of derivative instruments, if any, is expected to consist primarily of put and call options on securities and securities indices. Cash is a residual of the investment process. When the Subadviser is unable to find investment opportunities that meet the Fund’s criteria, the Fund’s cash balances may increase. The Fund is classified as non-diversified. The Subadviser’s investment philosophy is based upon its proprietary Absolute Value® approach, which seeks to provide attractive, sustainable, low volatility returns over the long term, while reducing downside portfolio risk. When the Fund takes a long position, it purchases a stock outright. The Fund takes long positions in securities that the Subadviser believes will rise in value. For long positions, the Subadviser seeks to identify companies it believes have certain characteristics including: Security price that is at a discount to assessed valuation as determined by the Subadviser’s unique and proprietary Absolute Value® approach Attractive business model Shareholder-oriented management Financial strength Undiscovered, under-followed, misunderstood The Fund takes short positions in securities that the Subadviser believes will go down in value. For short positions, the Subadviser seeks to identify companies it believes have certain characteristics including: Challenged business model Low price and earnings momentum Financial weakness Poor shareholder-orientation Security price that is at a premium to assessed valuation as determined by the Subadviser’s unique and proprietary Absolute Value® approach When the Fund takes a short position, it sells a security that it does not own at the current market price in anticipation that the market price will go down. To complete a short sale, the Fund must borrow the security from a broker or other counterparty, which may be the Fund’s custodian, to make delivery to the buyer. The Fund is then obligated to replace the borrowed security by purchasing the security in the open market at the time of closing out the short sale. The price at such time may be more or less than at the time the security was sold short. Until the borrowed security is returned, the Fund is required to pay the lender amounts equal to any dividends or interest that accrue during the period of the loan. To borrow the security, the Fund also may be required to pay a premium to the lender, which would increase the cost to the Fund of taking the short position. The proceeds of the short sale will be retained by the broker or other counterparty to the extent necessary to meet margin requirements until the short position is closed. The Fund’s net market exposure will fluctuate with market opportunities but will generally be between 10% and 90%. To seek to manage risk the Subadviser may use controls and techniques to systemically reduce market exposure upon the occurrence of certain trigger events. The Subadviser’s investment process generally results in high portfolio turnover.
Risk [Heading]	rr_RiskHeading	<b>PRINCIPAL RISKS</b>
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	There is the risk that you may lose money on your investment. All investments carry a certain amount of risk, and the Fund cannot guarantee that it will achieve its investment objective. An investment in the Fund is not a deposit or obligation of any bank, is not endorsed or guaranteed by any bank, and is not insured by the Federal Deposit Insurance Corporation (“FDIC”) or any other government agency. Below are some of the risks of investing in the Fund. The risks are described in alphabetical order and not in the order of importance or potential exposure. Convertible Securities Risk— convertible preferred stocks, which are convertible into shares of the issuer’s common stock and pay regular dividends, and convertible debt securities, which are convertible into shares of the issuer’s common stock and bear interest, are subject to the risks of equity securities and fixed income securities. The lower the conversion premium, the more likely the price of the convertible security will follow the price of the underlying common stock. Conversely, higher premium convertible securities are more likely to exhibit the behavior of bonds because the likelihood of conversion is lower, which may cause their prices to fall as interest rates rise. There is the risk that the issuer of convertible preferred stock will not be able to make dividend payments or that the issuer of a convertible bond will not be able to make principal and/or interest payments. Currency Risk—fluctuations in exchange rates may affect the total loss or gain on a non-U.S. dollar investment when converted back to U.S. dollars and exposure to non-U.S. currencies may subject the Fund to the risk that those currencies will decline in value relative to the U.S. dollar. Derivatives Risk—the use of derivatives involves costs, the risk that the value of derivatives may not correlate perfectly with their underlying assets, rates or indices, and the risk of mispricing or improper valuation. The use of derivatives may not succeed for various reasons, and the complexity and rapidly changing structure of derivatives markets may increase the possibility of market losses. Exchange-Traded Fund Risk—because exchange-traded funds incur their own costs, investing in them could result in a higher cost to the investor. Foreign Investment Risk—investments in foreign issuers involve additional risks (such as risks arising from less frequent trading, changes in political or social conditions, and less publicly available information about non-U.S. issuers) that differ from those associated with investments in U.S. issuers and may result in greater price volatility. High Cash Balance Risk— when the Fund has a significant cash balance for a sustained period, the benefit to the Fund of any market upswing may likely be reduced, and the Fund’s performance may be adversely affected. High Portfolio Turnover Risk—higher portfolio turnover may adversely affect Fund performance by increasing Fund transaction costs and may increase a shareholder’s tax liability. Liquidity Risk—the Fund may not be able to dispose of particular investments, such as illiquid securities, readily at favorable times or prices or the Fund may have to sell them at a loss. Management Risk—because the Fund is an actively managed investment portfolio, security selection or focus on securities in a particular style, market sector or group of companies may cause the Fund to incur losses or underperform relative to its benchmarks or other funds with a similar investment objective. There can be no guarantee that the Subadviser’s investment techniques and risk analysis will produce the desired result. Market Risk—market prices of investments held by the Fund may fall rapidly or unpredictably due to a variety of factors, including economic, political, or market conditions or in response to events that affect particular industries or companies. Master Limited Partnerships— investments in master limited partnerships are subject to similar risks to those associated with the specific industry or industries in which the partnership invests, such as the risk of investing in the real estate or oil and gas industries. In addition, investments in master limited partnerships are subject to the risks of investing in a partnership, including limited control and voting rights on matters affecting the partnership and fewer investor protections compared to corporations. Non-Diversified Fund Risk—the Fund is non-diversified and therefore a greater percentage of holdings may be focused in a small number of issuers or a single issuer, which can place the Fund at greater risk. Notwithstanding the Fund’s status as a “non-diversified” investment company under the Investment Company Act of 1940 (the “1940 Act”), the Fund intends to qualify as a regulated investment company accorded special tax treatment under the Internal Revenue Code of 1986, as amended (the “Internal Revenue Code”), which imposes its own diversification requirements that are less restrictive than the requirements applicable to “diversified” investment companies under the 1940 Act. The Fund’s intention to qualify as a regulated investment company may limit its pursuit of its investment strategy and its investment strategy could limit its ability to so qualify. PTP Risk— investing in PTPs (including master limited partnerships) involves special risks in addition to those typically associated with publicly traded companies. PTPs are exposed to the risks of their underlying assets, which in many cases includes the same types of risks as energy and natural resources companies, such as commodity pricing risk, supply and demand risk and depletion and exploration risk. PTPs are also subject to capital markets risk, which is the risk that they may be unable to raise capital to execute their growth strategies. PTPs are also subject to tax risk, which is the risk that PTPs may lose their partnership status for tax purposes. The Fund’s ability to make investments in certain PTPs, including master limited partnerships, can be limited by the Fund’s intention to qualify as a regulated investment company, and if the Fund does not appropriately limit such investments or if such investments are recharacterized for U.S. federal income tax purposes, the Fund’s status as a regulated investment company may be jeopardized. Real Estate Industry Risk—investments in the Fund may be subject to many of the same risks as a direct investment in real estate. The stock prices of companies in the real estate industry, including REITs, are typically sensitive to changes in real estate values, property taxes, interest rates, cash flow of underlying real estate assets, occupancy rates, government regulations affecting zoning, land use, and rents, as well as the management skill and creditworthiness of the issuer. REITs also depend generally on their ability to generate cash flow to make distributions to shareholders or unitholders and are subject to the risk of failing to qualify for favorable tax treatment under the Internal Revenue Code. Sector Risk—issuers and companies that are in similar industry sectors may be similarly affected by particular economic or market events; to the extent the Fund has substantial holdings within a particular sector, the risks associated with that sector increase. Stocks in the consumer discretionary and information technology sectors may comprise a significant portion of the Fund's portfolio.  The consumer discretionary sector may be affected by the performance of the overall economy, consumer confidence and spending, changes in demographics and consumer tastes, interest rates, and competitive pressures. The information technology sector may be affected by technological obsolescence, short product cycles, falling prices and profits, competitive pressures and general market conditions. Short Sales Risk—a short sale of a security involves the theoretical risk of unlimited loss because of potential unlimited increases in the market price of the security sold short. The Fund’s use of short sales, in certain circumstances, can result in significant losses. Small- and Mid-Capitalization Stock Risk—the stocks of small- and mid-capitalization companies often have greater price volatility, lower trading volume, and less liquidity than the stocks of larger, more established companies. Value Stock Risk—value stocks may perform differently from the market as a whole and may be undervalued by the market for a long period of time.
Risk Lose Money [Text]	rr_RiskLoseMoney	There is the risk that you may lose money on your investment.
Risk Not Insured Depository Institution [Text]	rr_RiskNotInsuredDepositoryInstitution	An investment in the Fund is not a deposit or obligation of any bank, is not endorsed or guaranteed by any bank, and is not insured by the Federal Deposit Insurance Corporation (“FDIC”) or any other government agency.
Risk Nondiversified Status [Text]	rr_RiskNondiversifiedStatus	<b>Non-Diversified Fund Risk</b>—the Fund is non-diversified and therefore a greater percentage of holdings may be focused in a small number of issuers or a single issuer, which can place the Fund at greater risk. Notwithstanding the Fund’s status as a “non-diversified” investment company under the Investment Company Act of 1940 (the “1940 Act”), the Fund intends to qualify as a regulated investment company accorded special tax treatment under the Internal Revenue Code of 1986, as amended (the “Internal Revenue Code”), which imposes its own diversification requirements that are less restrictive than the requirements applicable to “diversified” investment companies under the 1940 Act. The Fund’s intention to qualify as a regulated investment company may limit its pursuit of its investment strategy and its investment strategy could limit its ability to so qualify.
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	<b>PERFORMANCE</b>
Performance Narrative [Text Block]	rr_PerformanceNarrativeTextBlock	The following performance information illustrates 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 performance compares to that of two broad-based securities market indices. As always, past performance of the Fund (before and after taxes) is not an indication of how the Fund will perform in the future. To obtain updated performance information please visit www.amgfunds.com or call 800.548.4539.
Performance Information Illustrates Variability of Returns [Text]	rr_PerformanceInformationIllustratesVariabilityOfReturns	The following performance information illustrates 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 performance compares to that of two broad-based securities market indices.
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	800.548.4539
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	www.amgfunds.com
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	As always, past performance of the Fund (before and after taxes) is not an indication of how the Fund will perform in the future.
Bar Chart [Heading]	rr_BarChartHeading	Calendar Year Total Returns as of 12/31/18 (Class N)
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	Best Quarter: 6.75% (1st Quarter 2013) Worst Quarter: -4.39% (4th Quarter 2018)
Performance Table Heading	rr_PerformanceTableHeading	Average Annual Total Returns as of 12/31/18
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	Actual after-tax returns depend on an investor’s tax situation and may differ from those shown. After-tax returns are not relevant to investors who hold their Fund shares through tax-advantaged arrangements, such as 401(k) plans or individual retirement accounts (“IRAs”).
Performance Table One Class of after Tax Shown [Text]	rr_PerformanceTableOneClassOfAfterTaxShown	After-tax returns are shown for Class N shares only, and after-tax returns for Class I and Class Z shares will vary.
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 are not relevant to investors who hold their Fund shares through tax-advantaged arrangements, such as 401(k) plans or individual retirement accounts (“IRAs”). After-tax returns are shown for Class N shares only, and after-tax returns for Class I and Class Z shares will vary.
AMG River Road Long-Short Fund | Class N
Risk/Return:	rr_RiskReturnAbstract
Management Fee	rr_ManagementFeesOverAssets	0.85%	[1]
Distribution and Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Dividend and Interest Expense on Short Sales	rr_Component1OtherExpensesOverAssets	0.90%	[1]
Other Operating Expenses	rr_Component2OtherExpensesOverAssets	0.62%	[1]
Total Other Expenses	rr_OtherExpensesOverAssets	1.52%	[1]
Acquired Fund Fees and Expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.10%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	2.72%	[2]
Fee Waiver and Expense Reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.27%)	[3]
Total Annual Fund Operating Expenses After Fee Waiver and Expense Reimbursements	rr_NetExpensesOverAssets	2.45%	[2],[3]
1 Year	rr_ExpenseExampleYear01	$ 248
3 Years	rr_ExpenseExampleYear03	819
5 Years	rr_ExpenseExampleYear05	1,416
10 Years	rr_ExpenseExampleYear10	$ 3,031
2012	rr_AnnualReturn2012	9.58%
2013	rr_AnnualReturn2013	17.95%
2014	rr_AnnualReturn2014	(2.29%)
2015	rr_AnnualReturn2015	0.17%
2016	rr_AnnualReturn2016	4.36%
2017	rr_AnnualReturn2017	8.88%
2018	rr_AnnualReturn2018	(4.92%)
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	Best Quarter:
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Mar. 31, 2013
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	6.75%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	Worst Quarter:
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Dec. 31, 2018
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(4.39%)
1 Year	rr_AverageAnnualReturnYear01	(4.92%)
5 Years	rr_AverageAnnualReturnYear05	1.12%
Since Inception	rr_AverageAnnualReturnSinceInception	4.13%	[4]
Inception Date	rr_AverageAnnualReturnInceptionDate	May 04, 2011
AMG River Road Long-Short Fund | Class I
Risk/Return:	rr_RiskReturnAbstract
Management Fee	rr_ManagementFeesOverAssets	0.85%	[1]
Distribution and Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Dividend and Interest Expense on Short Sales	rr_Component1OtherExpensesOverAssets	0.90%	[1]
Other Operating Expenses	rr_Component2OtherExpensesOverAssets	0.62%	[1]
Total Other Expenses	rr_OtherExpensesOverAssets	1.52%	[1]
Acquired Fund Fees and Expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.10%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	2.47%	[2]
Fee Waiver and Expense Reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.27%)	[3]
Total Annual Fund Operating Expenses After Fee Waiver and Expense Reimbursements	rr_NetExpensesOverAssets	2.20%	[2],[3]
1 Year	rr_ExpenseExampleYear01	$ 223
3 Years	rr_ExpenseExampleYear03	744
5 Years	rr_ExpenseExampleYear05	1,291
10 Years	rr_ExpenseExampleYear10	$ 2,786
1 Year	rr_AverageAnnualReturnYear01	(4.62%)
5 Years	rr_AverageAnnualReturnYear05	1.40%
Since Inception	rr_AverageAnnualReturnSinceInception	3.16%	[5]
Inception Date	rr_AverageAnnualReturnInceptionDate	Mar. 04, 2013
AMG River Road Long-Short Fund | Class Z
Risk/Return:	rr_RiskReturnAbstract
Management Fee	rr_ManagementFeesOverAssets	0.85%	[1]
Distribution and Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Dividend and Interest Expense on Short Sales	rr_Component1OtherExpensesOverAssets	0.90%	[1]
Other Operating Expenses	rr_Component2OtherExpensesOverAssets	0.54%	[1]
Total Other Expenses	rr_OtherExpensesOverAssets	1.44%	[1]
Acquired Fund Fees and Expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.10%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	2.39%	[2]
Fee Waiver and Expense Reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.27%)	[3]
Total Annual Fund Operating Expenses After Fee Waiver and Expense Reimbursements	rr_NetExpensesOverAssets	2.12%	[2],[3]
1 Year	rr_ExpenseExampleYear01	$ 215
3 Years	rr_ExpenseExampleYear03	720
5 Years	rr_ExpenseExampleYear05	1,251
10 Years	rr_ExpenseExampleYear10	$ 2,706
1 Year	rr_AverageAnnualReturnYear01	(4.54%)
5 Years	rr_AverageAnnualReturnYear05
Since Inception	rr_AverageAnnualReturnSinceInception	(2.78%)	[6]
Inception Date	rr_AverageAnnualReturnInceptionDate	Sep. 29, 2017
AMG River Road Long-Short Fund | Return After Taxes on Distributions | Class N
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	(6.28%)
5 Years	rr_AverageAnnualReturnYear05	0.49%
Since Inception	rr_AverageAnnualReturnSinceInception	3.37%	[4]
Inception Date	rr_AverageAnnualReturnInceptionDate	May 04, 2011
AMG River Road Long-Short Fund | Return After Taxes on Distributions and Sale of Fund Shares | Class N
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	(1.95%)
5 Years	rr_AverageAnnualReturnYear05	0.79%
Since Inception	rr_AverageAnnualReturnSinceInception	3.07%	[4]
Inception Date	rr_AverageAnnualReturnInceptionDate	May 04, 2011
AMG River Road Long-Short Fund | Russell 3000® Index (reflects no deduction for fees, expenses, or taxes) | Class N
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	(5.24%)
5 Years	rr_AverageAnnualReturnYear05	7.91%
Since Inception	rr_AverageAnnualReturnSinceInception	10.26%	[4]
Inception Date	rr_AverageAnnualReturnInceptionDate	May 04, 2011
AMG River Road Long-Short Fund | Russell 3000® Index (reflects no deduction for fees, expenses, or taxes) | Class I
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	(5.24%)
5 Years	rr_AverageAnnualReturnYear05	7.91%
Since Inception	rr_AverageAnnualReturnSinceInception	10.87%	[5]
Inception Date	rr_AverageAnnualReturnInceptionDate	Mar. 04, 2013
AMG River Road Long-Short Fund | Russell 3000® Index (reflects no deduction for fees, expenses, or taxes) | Class Z
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	(5.24%)
5 Years	rr_AverageAnnualReturnYear05
Since Inception	rr_AverageAnnualReturnSinceInception	0.61%	[6]
Inception Date	rr_AverageAnnualReturnInceptionDate	Sep. 29, 2017
AMG River Road Long-Short Fund | 50% Russell 3000® Index/50% ICE BofAML 3-Month U.S. Treasury Bill Index (reflects no deduction for taxes, expenses or fees.) | Class N
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	(1.42%)
5 Years	rr_AverageAnnualReturnYear05	4.42%
Since Inception	rr_AverageAnnualReturnSinceInception	5.52%	[4]
Inception Date	rr_AverageAnnualReturnInceptionDate	May 04, 2011
AMG River Road Long-Short Fund | 50% Russell 3000® Index/50% ICE BofAML 3-Month U.S. Treasury Bill Index (reflects no deduction for taxes, expenses or fees.) | Class I
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	(1.42%)
5 Years	rr_AverageAnnualReturnYear05	4.42%
Since Inception	rr_AverageAnnualReturnSinceInception	5.79%	[5]
Inception Date	rr_AverageAnnualReturnInceptionDate	Mar. 04, 2013
AMG River Road Long-Short Fund | 50% Russell 3000® Index/50% ICE BofAML 3-Month U.S. Treasury Bill Index (reflects no deduction for taxes, expenses or fees.) | Class Z
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	(1.42%)
5 Years	rr_AverageAnnualReturnYear05
Since Inception	rr_AverageAnnualReturnSinceInception	1.44%	[6]
Inception Date	rr_AverageAnnualReturnInceptionDate	Sep. 29, 2017

[1] Expense information has been restated to reflect current fees.

[2] The Total Annual Fund Operating Expenses and Total Annual Fund Operating Expenses After Fee Waiver and Expense Reimbursements do not correlate to the ratios of expenses to average net assets in the Financial Highlights section of this Prospectus, which reflect only the operating expenses of the Fund and do not include fees and expenses of any acquired fund.

[3] AMG Funds LLC (the “Investment Manager”) has contractually agreed, through at least March 1, 2020, to waive management fees and/or pay or reimburse the Fund’s expenses in order to limit Total Annual Fund Operating Expenses After Fee Waiver and Expense Reimbursements (exclusive of taxes, interest (including interest incurred in connection with bank and custody overdrafts and in connection with securities sold short), shareholder servicing fees, distribution and service (12b-1) fees, brokerage commissions and other transaction costs, dividends payable with respect to securities sold short, acquired fund fees and expenses, and extraordinary expenses) of the Fund to the annual rate of 1.12% of the Fund’s average daily net assets (this annual rate or such other annual rate that may be in effect from time to time, the “Expense Cap”), subject to later reimbursement by the Fund in certain circumstances. In general, for a period of up to 36 months after the date any amounts are paid, waived or reimbursed by the Investment Manager, the Investment Manager may recover such amounts from the Fund, provided that such repayment would not cause the Fund’s Total Annual Fund Operating Expenses After Fee Waiver and Expense Reimbursements (exclusive of the items noted in the parenthetical above) to exceed either (i) the Expense Cap in effect at the time such amounts were paid, waived or reimbursed, or (ii) the Expense Cap in effect at the time of such repayment by the Fund. The contractual expense limitation may only be terminated in the event the Investment Manager or a successor ceases to be the investment manager of the Fund or a successor fund, by mutual agreement between the Investment Manager and the AMG Funds IV Board of Trustees or in the event of the Fund’s liquidation unless the Fund is reorganized or is a party to a merger in which the surviving entity is successor to the accounting and performance information of the Fund.

[4] Class N and Index performance shown reflects performance since the inception date of the Fund’s Class N shares on May 4, 2011.

[5] Class I and Index performance shown reflects performance since the inception date of the Fund’s Class I shares on March 4, 2013.

[6] Class Z and Index performance shown reflects performance since the inception date of the Fund’s Class Z shares on September 29, 2017.