2.4.0.8020006 - Disclosure - Risk/Return Detail Data {Elements} - The Merger Fundtruetruefalse1false falsefalseS000005158Memberhttp://www.sec.gov/CIK0000701804duration2012-12-31T00:00:002012-12-31T00:00:00pureStandardhttp://www.xbrl.org/2003/instancepurexbrli01true 3rr_RiskReturnAbstractrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Risk/Return:2false 4rr_RiskReturnHeadingrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1falsefalsefalse00The Merger Fundfalsefalsefalsexbrli: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 4rr_ObjectiveHeadingrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1falsefalsefalse00Investment Objective:falsefalsefalsexbrli:stringItemTypestringInvestment Objectives/Goals. Disclose the Fund's investment objectives or goals. A Fund also may identify its type or category (e.g., that it is a Money Market Fund or a balanced fund).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 2 -Subsection a false0Objective [Heading]4false 4rr_ObjectivePrimaryTextBlockrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1falsefalsefalse00<div align="justify" style="TEXT-INDENT: 0pt; DISPLAY: block; MARGIN-LEFT: 0pt; MARGIN-RIGHT: 0pt"><font style="DISPLAY: inline; FONT-FAMILY: Times New Roman; FONT-SIZE: 10pt">  The Merger Fund (the “Fund”) seeks to achieve capital growth by engaging in merger arbitrage.</font> </div>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 4rr_ExpenseHeadingrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1falsefalsefalse00Fees and Expenses of the Fund:falsefalsefalsexbrli:stringItemTypestringRisk/Return Summary Fee Table Includes the following information, in plain English under rule 421(d) under the Securities Act, after Item 2 Fees and expenses of the Fund This table describes the fees and expenses that you may pay if you buy and hold shared of the Fund. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $[_____] in [name of fund family] funds. Shareholder Fees (fees paid directly from your investment) Example This Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Fund for the time periods indicated and then you redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return per year and that the Fund's operating expenses remained the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be You would pay the following expenses if you did not redeem your shares The Example does not reflect sales charges (loads) on reinvested dividends [and other distributions]. If these sales charges (loads) were included, your costs would be higher. Portfolio Turnover The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover may indicate higher transaction costs. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was __% of the average value of its whole portfolio. Instructions. A.3.instructions.6 New Funds. For purposes of this Item, a "New Fund" is a Fund that does not include in Form N-1A financial statements reporting operating results or that includes financial statements for the Fund's initial fiscal year reporting operating results for a period of 6 months or less. The following Instructions apply to New Funds.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection instructions -Paragraph 1 -Subparagraph d false0Expense [Heading]6false 4rr_ExpenseNarrativeTextBlockrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1falsefalsefalse00<div align="left" style="TEXT-INDENT: 0pt; DISPLAY: block; MARGIN-LEFT: 0pt; MARGIN-RIGHT: 0pt"><font style="DISPLAY: inline; FONT-FAMILY: Times New Roman; FONT-SIZE: 10pt">  The table below describes the fees and expenses that you may pay if you buy and hold shares of the Fund.</font> </div>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 4rr_ShareholderFeesCaptionrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1falsefalsefalse00 Shareholder Fees (fees paid directly from your investment) falsefalsefalsexbrli:stringItemTypestringShareholder Fees (fees paid directly from your investment).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection table -Paragraph 1 false0Shareholder Fees Caption [Text]8false 4rr_OperatingExpensesCaptionrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1falsefalsefalse00 Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment) falsefalsefalsexbrli:stringItemTypestringAnnual Fund Operating Expenses (ongoing expenses that you pay each year as a percentage of the value of your investment)Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection table -Paragraph 1 -Subparagraph 7 false0Operating Expenses Caption [Text]9false 4rr_FeeWaiverOrReimbursementOverAssetsDateOfTerminationrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1falsefalsefalse002014-07-08falsefalsefalsexbrli:stringItemTypestringThis element represents the date of expected termination of any expense reimbursement or fee waiver arrangements that reduce any Fund operating expenses (SEC Form N-1A 2006-09-14 A.3.table.1.11 Total Annual Fund Operating Expenses A.3.instructions.3.e).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection instructions -Paragraph 3 -Subparagraph e false0Fee Waiver or Reimbursement over Assets, Date of Termination10false 4rr_PortfolioTurnoverHeadingrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1falsefalsefalse00Portfolio Turnoverfalsefalsefalsexbrli:stringItemTypestringDisclose the portfolio turnover rate provided in response to Item 14(a) for the most recent fiscal year (or for such shorter period as the Fund has been in operation). Disclose the period for which the information is provided if less than a full fiscal year. A Fund that is a Money Market Fund may omit the portfolio turnover information required by this Item.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection instructions -Paragraph 5 false0Portfolio Turnover [Heading]11false 4rr_PortfolioTurnoverTextBlockrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1falsefalsefalse00<div style="TEXT-INDENT: 36pt; DISPLAY: block; MARGIN-LEFT: 0pt; MARGIN-RIGHT: 0pt" align="justify"> <font style="DISPLAY: inline; FONT-FAMILY: Times New Roman; FONT-SIZE: 10pt">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 the Annual Fund Operating Expenses table above or in the Example, affect the Fund’s performance.  During the fiscal year ended December 31, 2012, the Fund’s portfolio turnover rate was 240.32% of the average value of its portfolio.</font> </div>falsefalsefalsenonnum:textBlockItemTypenaDisclose the portfolio turnover rate provided in response to Item 14(a) for the most recent fiscal year (or for such shorter period as the Fund has been in operation). Disclose the period for which the information is provided if less than a full fiscal year. A Fund that is a Money Market Fund may omit the portfolio turnover information required by this Item.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection example -Paragraph 3 false0Portfolio Turnover [Text Block]12false 4rr_PortfolioTurnoverRaterr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1truetruefalse2.40322.4032falsefalsefalsexbrli:pureItemTypepureThis element represents the rate of portfolio turnover presented as a percentage (SEC Form N-1A 2006-09-14 A.3.example.3 Portfolio Turnover A.3.instructions.5 Portfolio Turnover).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection example -Paragraph 3 false0Portfolio Turnover, Rate13false 4rr_ExpensesNotCorrelatedToRatioDueToAcquiredFundFeesrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1falsefalsefalse00The operating expenses in this fee table may not correlate to the expense ratio in the Fund's financial highlights because the financial statements include only the direct operating expenses incurred by the Fund, not the indirect costs of investing in other investment companies.falsefalsefalsexbrli:stringItemTypestringThe Fund may clarify in a footnote to the fee table that the total annual fund operating expenses under Item 3 do not correlate to the ratio of expenses to average net assets given in response to Item 8, which reflects the operating expenses of the Fund and does not include Acquired Fund fees and 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 f -Clause vii false0Expenses Not Correlated to Ratio Due to Acquired Fund Fees [Text]14false 4rr_ExpenseExampleHeadingrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1falsefalsefalse00Examplefalsefalsefalsexbrli: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]15false 4rr_ExpenseExampleNarrativeTextBlockrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1falsefalsefalse00<div align="justify" style="TEXT-INDENT: 36pt; DISPLAY: block; MARGIN-LEFT: 0pt; MARGIN-RIGHT: 0pt"> <font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt">The example below is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.  The example assumes that you invest $10,000 in the Fund for the time periods indicated, and then redeem all of your shares at the end of those periods.  The example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses remain the same.  Only the first year of each period in the example takes into account the fee waiver described above.</font></div>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]16false 4rr_ExpenseExampleByYearCaptionrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1falsefalsefalse00Although your actual costs may be higher or lower, based on these assumptions, your costs would be: falsefalsefalsexbrli:stringItemTypestringThe 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 false0Expense Example by, Year, Caption [Text]17false 4rr_StrategyHeadingrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1falsefalsefalse00Principal Investment Strategiesfalsefalsefalsexbrli:stringItemTypestringPrincipal investment strategies of the Fund. Summarize how the Fund intends to achieve its investment objectives by identifying the Fund's principal investment strategies (including the type or types of securities in which the Fund invests or will invest principally) and any policy to concentrate in securities of issuers in a particular industry or group of industries.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection a false0Strategy [Heading]18false 4rr_StrategyNarrativeTextBlockrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1falsefalsefalse00<div style="TEXT-INDENT: 36pt; DISPLAY: block; MARGIN-LEFT: 0pt; MARGIN-RIGHT: 0pt" align="justify"> <font style="DISPLAY: inline; FONT-FAMILY: Times New Roman; FONT-SIZE: 10pt">Under normal market conditions, the Fund invests at least 80% of its total assets principally in the common stock, preferred stock and, occasionally, warrants of companies which are involved in publicly announced mergers, takeovers, tender offers, leveraged buyouts, spin-offs, liquidations and other corporate reorganizations.  Merger arbitrage is a highly specialized investment approach generally designed to profit from the successful completion of such transactions.  Although a variety of strategies may be employed depending upon the nature of the reorganizations selected for investment, the most common merger-arbitrage activity involves purchasing the shares of an announced acquisition target at a discount to their expected value upon completion of the acquisition. <font style="DISPLAY: inline"> The size of this discount, known as the arbitrage “spread,” generally determines the Fund’s potential profit on any given investment.  Because Westchester Capital Management, LLC (the “Adviser”) seeks to profit from the “spread” described above upon the completion of a merger, takeover or other reorganization rather than the performance of the market overall or any one issuer, the Adviser believes the merger-arbitrage strategy is designed to provide performance that normally has low correlation with the performance of stock markets.</font></font> </div> <br/><div style="TEXT-INDENT: 36pt; DISPLAY: block; MARGIN-LEFT: 0pt; MARGIN-RIGHT: 0pt" align="justify"> <font style="DISPLAY: inline; FONT-FAMILY: Times New Roman; FONT-SIZE: 10pt">In conjunction with investment in an acquisition target or other investment, the Fund may employ a variety of hedging strategies to protect against issuer-related risk or other risks, including selling short the securities of the company that proposes to acquire the acquisition target and/or the purchase and sale of put and call options.  The Fund may enter into derivative transactions and other instruments of any kind for hedging purposes, duration or volatility management purposes, or otherwise to gain, or reduce, long or short exposure to one or more asset classes or issuers.  For example, the Adviser may seek to hedge the Fund’s portfolio against a decline in the value of its portfolio securities or a decline in the market generally by purchasing put options.  </font> </div> <br/><div style="TEXT-INDENT: 36pt; DISPLAY: block; MARGIN-LEFT: 0pt; MARGIN-RIGHT: 0pt" align="justify"> <font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt">In pursuing the Fund’s investment objective and strategies, the Fund may invest in U.S. and foreign securities without limit.  The Fund engages in active trading and may invest a portion of its assets to seek short-term capital appreciation.</font> </div> <br/><div style="TEXT-INDENT: 36pt; DISPLAY: block; MARGIN-LEFT: 0pt; MARGIN-RIGHT: 0pt" align="justify"> <font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt">The Fund may invest in other investment companies, including exchange-traded funds (ETFs).  To the extent that the Fund invests in shares of another investment company or ETF, the Fund bears its proportionate share of the expenses of the underlying investment company or ETF and is subject to the risks of the underlying investment company’s or ETF’s investments.</font> </div> <br/><div style="TEXT-INDENT: 36pt; DISPLAY: block; MARGIN-LEFT: 0pt; MARGIN-RIGHT: 0pt" align="justify"> <font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt">In making merger arbitrage investments for the Fund, the Adviser is guided by the following general principles: (1) securities are purchased only after a reorganization is announced or when one or more publicly disclosed events point toward the possibility of some type of merger or other significant corporate event within a reasonable period of time; (2) before an initial position is established, a preliminary analysis is made of the expected transaction to determine the probability and timing of a successful completion; (3) in deciding whether or to what extent to invest, the Adviser evaluates, among other things, the credibility, strategic motivation and financial resources of the participants, and the liquidity of the securities involved in the transaction; (4) the risk-reward characteristics of each arbitrage position are assessed on an ongoing basis, and the Fund’s holdings may be adjusted at any time; and (5) the Adviser may invest the Fund’s assets in both negotiated, or “friendly,” reorganizations and non-negotiated, or “hostile,” takeover attempts, but in either case the Adviser’s primary considerations include the likelihood that the transaction will be successfully completed and its risk-adjusted profile.  The Adviser may sell securities at any time, including if the Adviser’s evaluation of the risk/reward ratio is no longer favorable.</font> </div>falsefalsefalsenonnum:textBlockItemTypenaPrincipal investment strategies of the Fund. Summarize how the Fund intends to achieve its investment objectives by identifying the Fund's principal investment strategies (including the type or types of securities in which the Fund invests or will invest principally) and any policy to concentrate in securities of issuers in a particular industry or group of industries.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection a false0Strategy Narrative [Text Block]19false 4rr_RiskHeadingrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1falsefalsefalse00Principal Risks:falsefalsefalsexbrli:stringItemTypestringNarrative Risk Disclosure.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 1 false0Risk [Heading]20false 4rr_RiskNarrativeTextBlockrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1falsefalsefalse00<div align="justify" style="TEXT-INDENT: 0pt; DISPLAY: block; MARGIN-LEFT: 0pt; MARGIN-RIGHT: 0pt"><font style="DISPLAY: inline; FONT-FAMILY: Times New Roman; FONT-SIZE: 10pt">  You could lose money by investing in the Fund.  Although the Fund will strive to meet its investment objective, there is no assurance that it will do so.  Many factors affect the Fund’s net asset value and performance, including the following:</font> </div> <br/><div style="TEXT-INDENT: 0pt; DISPLAY: block; MARGIN-LEFT: 0pt; MARGIN-RIGHT: 0pt" align="justify"> <font style="DISPLAY: inline; FONT-FAMILY: Times New Roman; FONT-SIZE: 10pt"><font style="FONT-STYLE: italic; DISPLAY: inline">Merger and Event-Driven Risk –</font> Merger-arbitrage and event-driven investing involves the risk that the Adviser’s evaluation of the outcome of a proposed event, whether it be a merger, reorganization, regulatory issue or other event, will prove incorrect and that the Fund’s return on the investment will be negative. Even if the Adviser’s judgment regarding the likelihood of a specific outcome proves correct, the expected event may be delayed or completed on terms other than those originally proposed, which may cause the Fund to lose money or fail to achieve a desired rate of return.  The Fund expects to employ strategies that are not designed to benefit from general market appreciation or improved economic conditions in the global economy.  Accordingly, the Fund may underperform the markets under certain market conditions, such as periods when there is rapid appreciation in the markets.</font> </div> <br/><div style="TEXT-INDENT: 0pt; DISPLAY: block; MARGIN-LEFT: 0pt; MARGIN-RIGHT: 0pt" align="justify"> <font style="DISPLAY: inline; FONT-FAMILY: Times New Roman; FONT-SIZE: 10pt"><font style="FONT-STYLE: italic; DISPLAY: inline">Hedging Transactions –</font> The success of the Fund’s hedging strategy will be subject to the Adviser’s ability to assess correctly the degree of correlation between the performance of the instruments used in the hedging strategy and the performance of the investments in the portfolio being hedged. Hedging transactions involve the risk of imperfect correlation.  Imperfect correlation may prevent the Fund from achieving the intended hedge or expose the Fund to risk of loss.  Hedging transactions also limit the opportunity for gain if the value of a hedged portfolio position should increase.</font> </div> <br/><div style="TEXT-INDENT: 0pt; DISPLAY: block; MARGIN-LEFT: 0pt; MARGIN-RIGHT: 0pt" align="justify"> <font style="DISPLAY: inline; FONT-FAMILY: Times New Roman; FONT-SIZE: 10pt"><font style="FONT-STYLE: italic; DISPLAY: inline">Management Risk –</font> The Fund is subject to management risk because it is an actively managed investment portfolio.  The Adviser will apply its investment techniques and risk analyses in making investment decisions for the Fund, but there is no guarantee that its decisions will produce the intended result or that its evaluation of the likelihood that a specific merger or reorganization will be completed as expected will prove correct.</font> </div> <br/><div style="TEXT-INDENT: 0pt; DISPLAY: block; MARGIN-LEFT: 0pt; MARGIN-RIGHT: 0pt" align="justify"> <font style="DISPLAY: inline; FONT-FAMILY: Times New Roman; FONT-SIZE: 10pt"><font style="FONT-STYLE: italic; DISPLAY: inline">Portfolio Turnover Risk –</font> <font style="DISPLAY: inline">The frequency of the Fund’s transactions will vary from year to year, though m</font>erger arbitrage portfolios typically have higher turnover rates than portfolios of typical long-only funds.<font style="DISPLAY: inline"> Increased portfolio turnover may result in higher brokerage commissions, dealer mark-ups and other transaction costs.  The higher costs associated with increased portfolio turnover may offset gains in the Fund’s performance.  </font>The sale of portfolio securities associated with portfolio turnover may also result in the recognition of capital gain, which will be taxable to shareholders (in the case of short-term capital gain, at ordinary income rates) when distributed to shareholders.</font> </div> <br/><div style="TEXT-INDENT: 0pt; DISPLAY: block; MARGIN-LEFT: 0pt; MARGIN-RIGHT: 0pt" align="justify"> <font style="DISPLAY: inline; FONT-FAMILY: Times New Roman; FONT-SIZE: 10pt"><font style="FONT-STYLE: italic; DISPLAY: inline">Derivatives Risk –</font> Financial derivatives, such as options, swaps and futures contracts, may not produce the desired investment results because they are not perfect substitutes for the underlying securities, indices or currencies from which they are derived. Derivatives may also create leverage which will amplify the effect of the performance of these instruments on the Fund and may produce significant losses.</font> </div> <br/><div style="TEXT-INDENT: 0pt; DISPLAY: block; MARGIN-LEFT: 0pt; MARGIN-RIGHT: 0pt" align="justify"> <font style="DISPLAY: inline; FONT-FAMILY: Times New Roman; FONT-SIZE: 10pt"><font style="FONT-STYLE: italic; DISPLAY: inline">Foreign Investing –</font> <font style="DISPLAY: inline">Investments in foreign countries</font> may entail political, cultural, regulatory, legal and tax risks different from those associated with comparable transactions in the United States.  Such investments <font style="DISPLAY: inline">are subject to currency risk and country-specific risks such as political, diplomatic, regional conflicts, terrorism, war, social and economic instability and policies that may have the effect of decreasing the value of foreign securities.  Foreign investments may be subject to foreign withholding taxes.  Also, foreign countries may be subject to different trading settlement practices, less government supervision, less publicly available information, limited trading markets and greater volatility than U.S. investments.  </font></font> </div> <br/><div style="TEXT-INDENT: 0pt; DISPLAY: block; MARGIN-LEFT: 0pt; MARGIN-RIGHT: 0pt" align="justify"> <font style="DISPLAY: inline; FONT-FAMILY: Times New Roman; FONT-SIZE: 10pt"><font style="FONT-STYLE: italic; DISPLAY: inline">Debt Securities Risk –</font> Debt securities may fluctuate in value due to, among other things, changes in interest rates, general economic conditions, industry fundamentals, market sentiment and the financial condition of the issuer, including the issuer’s credit rating or financial performance.  The market value of convertible debt securities will also be affected by changes in the price of the underlying equity securities.  The market values of debt securities issued by companies involved in pending corporate mergers, takeovers or other corporate events may be determined in large part by the status of the transaction and its eventual outcome, especially if the debt securities are subject to change of control provisions that entitle the holder to be paid par value or some other specified dollar amount upon completion of a transaction or other event.</font> </div> <br/><div style="TEXT-INDENT: 0pt; DISPLAY: block; MARGIN-LEFT: 0pt; MARGIN-RIGHT: 0pt" align="justify"> <font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt"><font style="FONT-STYLE: italic; DISPLAY: inline">Leveraging Risk –</font> The use of leverage, such as borrowing money to purchase securities, engaging in reverse repurchase agreements, lending portfolio securities and engaging in forward commitment transactions, will cause the value of the Fund’s shares to be more volatile.  Unless profits and income on securities acquired with leverage exceed the costs of the leverage, the use of leverage will diminish the investment performance of the Fund compared with what it would have been without leverage, and the use of leverage may magnify any losses associated with such transactions.</font> </div> <br/><div style="TEXT-INDENT: 0pt; DISPLAY: block; MARGIN-LEFT: 0pt; MARGIN-RIGHT: 0pt" align="justify"> <font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt"><font style="FONT-STYLE: italic; DISPLAY: inline">Short Selling Risk</font> – If the price of a security sold short increases between the time of the short sale and the time the Fund covers its short position, the Fund will incur a loss.  The amount of a potential loss on an uncovered short sale transaction is theoretically unlimited.  The Fund is required to deposit collateral in connection with such short sales and has to pay a fee to borrow particular securities and will often be obligated to pay over any dividends and accrued interest on borrowed securities.</font> </div> <br/><div style="TEXT-INDENT: 0pt; DISPLAY: block; MARGIN-LEFT: 0pt; MARGIN-RIGHT: 0pt" align="justify"> <font style="DISPLAY: inline; FONT-FAMILY: Times New Roman; FONT-SIZE: 10pt"><font style="FONT-STYLE: italic; DISPLAY: inline">Market Risk</font> <font style="FONT-STYLE: italic; DISPLAY: inline">–</font> Investment markets can be volatile. The prices of investments can fall rapidly in response to developments affecting a specific company or industry, or to changing economic, political or market conditions.  The Fund’s investments may decline in value if markets perform poorly.</font> </div>falsefalsefalsenonnum:textBlockItemTypenaNarrative Risk Disclosure. A Fund may, in responding to this Item, describe the types of investors for whom the Fund is intended or the types of investment goals that may be consistent with an investment in the Fund.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 1 -Subparagraph i -Clause instruction false0Risk Narrative [Text Block]21false 4rr_RiskLoseMoneyrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1falsefalsefalse00You could lose money by investing in the Fund.falsefalsefalsexbrli:stringItemTypestringSummarize the principal risks of investing in the Fund, including the risks to which the Fund's portfolio as a whole is subject and the circumstances reasonably likely to affect adversely the Fund's net asset value, yield, and total return. Unless the Fund is a Money Market Fund, disclose that loss of money is a risk of investing in the Fund. A Fund may, in responding to this Item, describe the types of investors for whom the Fund is intended or the types of investment goals that may be consistent with an investment in the Fund.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 1 -Subparagraph i false0Risk Lose Money [Text]22false 4rr_BarChartAndPerformanceTableHeadingrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1falsefalsefalse00Annual Total Returns: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]23false 4rr_PerformanceNarrativeTextBlockrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1falsefalsefalse00<div align="justify" style="TEXT-INDENT: 0pt; DISPLAY: block; MARGIN-LEFT: 0pt; MARGIN-RIGHT: 0pt"><font style="DISPLAY: inline; FONT-FAMILY: Times New Roman; FONT-SIZE: 10pt">  The information in the bar chart and table shown below provides some indication of the risks of investing in the Fund but does not reflect the deduction of taxes that a shareholder would pay on distributions or redemptions.  The bar chart shows changes in the Fund’s performance from year to year over a ten-year period for Investor Class shares and the table compares the average annual total returns of the Fund’s Investor Class shares for the 1-, 5- and 10- year periods with those of the S&P 500 Index, a broad measure of market performance.  After-tax returns are shown for Investor Class shares only; after-tax returns for other classes will vary.  As of the date of this Prospectus, no Institutional Class shares of the Fund are outstanding.  Institutional Class shares represent an investment in the same portfolio of securities as Investor Class shares.  Annual returns would differ only to the extent that Institutional Class shares do not have the same expenses as Investor Class shares.  Institutional Class shares are not subject to distribution and/or service (12b-1) fees.</font> </div> <br/><div style="TEXT-INDENT: 36pt; DISPLAY: block; MARGIN-LEFT: 0pt; MARGIN-RIGHT: 0pt" align="justify"> <font style="DISPLAY: inline; FONT-FAMILY: Times New Roman; FONT-SIZE: 10pt">Performance data included herein for periods prior to 2011 reflect that of Westchester Capital Management, Inc., the Fund’s prior investment adviser.  Messrs. Behren and Shannon, the Fund’s current portfolio managers, have served as co-portfolio managers of the Fund since January 2007.</font> </div> <br/><div style="text-indent: 36pt; display: block; margin-left: 0pt; margin-right: 0pt;" align="justify"> <font style="display: inline; font-family: Times New Roman; font-size: 10pt;">The Fund’s past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future.  Updated performance information is available on the Fund’s website at <font style="display: inline; text-decoration: underline;">http://www.mergerfund.com</font>.</font> </div>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]24false 4rr_PerformanceInformationIllustratesVariabilityOfReturnsrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1falsefalsefalse00The information in the bar chart and table shown below provides some indication of the risks of investing in the Fund but does not reflect the deduction of taxes that a shareholder would pay on distributions or redemptions.falsefalsefalsexbrli:stringItemTypestringInclude the bar chart and table required by paragraphs (b)(2)(ii) and (iii) of this section. Provide a brief explanation of how the information illustrates the variability of the Fund's returns (e.g., by stating that the information provides some indication of the risks of investing in the Fund by showing changes in the Fund's performance from year to year and by showing how the Fund's average annual returns for 1, 5, and 10 years compare with those of a broad measure of market performance). Provide a statement to the effect that the Fund's past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph i false0Performance Information Illustrates Variability of Returns [Text]25false 4rr_PerformanceAvailabilityWebSiteAddressrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1falsefalsefalse00http://www.mergerfund.comfalsefalsefalsexbrli:stringItemTypestringIf applicable, include a statement explaining that updated performance information is available and providing a Website address and/or toll-free (or collect) telephone number where the updated information may be obtained.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph i false0Performance Availability Website Address [Text]26false 4rr_PerformancePastDoesNotIndicateFuturerr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1falsefalsefalse00The Fund's past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future.falsefalsefalsexbrli:stringItemTypestringInclude the bar chart and table required by paragraphs (b)(2)(ii) and (iii) of this section. Provide a brief explanation of how the information illustrates the variability of the Fund's returns (e.g., by stating that the information provides some indication of the risks of investing in the Fund by showing changes in the Fund's performance from year to year and by showing how the Fund's average annual returns for 1, 5, and 10 years compare with those of a broad measure of market performance). Provide a statement to the effect that the Fund's past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph i false0Performance Past Does Not Indicate Future [Text]27false 4rr_BarChartHeadingrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1falsefalsefalse00Total return as of 12/31 for each yearfalsefalsefalsexbrli: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 [Heading]28false 4rr_BarChartClosingTextBlockrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1falsefalsefalse00<div style="TEXT-INDENT: 36pt; DISPLAY: block; MARGIN-LEFT: 0pt; MARGIN-RIGHT: 0pt" align="justify"> <font style="FONT-STYLE: italic; DISPLAY: inline; FONT-FAMILY: Times New Roman; FONT-SIZE: 10pt">During the ten-year period shown in the above chart, the highest quarterly return was 5.08% (for the quarter ended June 30, 2003) and the lowest quarterly return was -4.00% (for the quarter ended September 30, 2011).</font> </div> <br/><div style="TEXT-INDENT: 36pt; DISPLAY: block; MARGIN-LEFT: 0pt; MARGIN-RIGHT: 0pt" align="justify"> <font style="FONT-STYLE: italic; DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt">The calendar year-to-date performance of the Fund’s Investor Class shares as of June 30, 2013 is: 0.32%.</font> </div>falsefalsefalsenonnum:textBlockItemTypenaIf the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph ii false0Bar Chart Closing [Text Block]29false 4rr_BarChartReturnsForClassNotOfferedInProspectusrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1falsefalsefalse00The returns are for Investor Class shares of the Fund, which are not offered in this Prospectus. falsefalsefalsexbrli:stringItemTypestringWhen a Multiple Class Fund offering one or more Classes offers a new Class in a prospectus that does not offer the shares of any other Class, include the bar chart with annual total returns for any other existing Class for the first year that the Class is offered. Explain in a footnote that the returns are for a Class that is not offered in the prospectus that would have substantially similar annual returns because the shares are invested in the same portfolio of securities and the annual returns would differ only to the extent that the Classes do not have the same expenses. Include return information for the other Class reflected in the bar chart in the performance 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 -Subparagraph instructions -Clause 3 -Exhibit b false0Bar Chart, Returns for Class Not Offered in Prospectus [Text]30false 4rr_YearToDateReturnLabelrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1falsefalsefalse00year-to-date performancefalsefalsefalsexbrli:stringItemTypestringIf the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph ii false0Year to Date Return, Label31false 4rr_BarChartYearToDateReturnDaterr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1falsefalsefalse002013-06-30falsefalsetruexbrli:dateItemTypedateIf the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph ii false0Bar Chart, Year to Date Return, Date32false 4rr_BarChartYearToDateReturnrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1truetruefalse0.00320.0032falsefalsefalsexbrli:pureItemTypepureIf the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph ii false0Bar Chart, Year to Date Return33false 4rr_HighestQuarterlyReturnLabelrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1falsefalsefalse00highest quarterly returnfalsefalsefalsexbrli:stringItemTypestringIf the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph ii false0Highest Quarterly Return, Label34false 4rr_BarChartHighestQuarterlyReturnDaterr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1falsefalsefalse002003-06-30falsefalsetruexbrli:dateItemTypedateIf the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph ii false0Highest Quarterly Return, Date35false 4rr_BarChartHighestQuarterlyReturnrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1truetruefalse0.05080.0508falsefalsefalsexbrli:pureItemTypepureIf the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph ii false0Highest Quarterly Return36false 4rr_LowestQuarterlyReturnLabelrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1falsefalsefalse00lowest quarterly returnfalsefalsefalsexbrli:stringItemTypestringIf the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph ii false0Lowest Quarterly Return, Label37false 4rr_BarChartLowestQuarterlyReturnDaterr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1falsefalsefalse002011-09-30falsefalsetruexbrli:dateItemTypedateIf the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph ii false0Lowest Quarterly Return, Date38false 4rr_BarChartLowestQuarterlyReturnrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1truetruefalse-0.0400-0.0400falsefalsefalsexbrli:pureItemTypepureIf the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph ii false0Lowest Quarterly Return39false 4rr_IndexNoDeductionForFeesExpensesTaxesrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1falsefalsefalse00(reflects no deduction for fees, expenses or taxes)falsefalsefalsexbrli:stringItemTypestringThe Performance Table includes a parenthetical, indicating that the Index "(reflects no deduction for fees, expenses or taxes)". This tag is used when this is reflected in a footnote.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph iii -Clause 1 -Exhibit 5 false0Index No Deduction for Fees, Expenses, Taxes [Text]40false 4rr_PerformanceTableUsesHighestFederalRaterr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1falsefalsefalse00After-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.falsefalsefalsexbrli:stringItemTypestringProvide a brief explanation that 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.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph iii false0Performance Table Uses Highest Federal Rate41false 4rr_PerformanceTableNotRelevantToTaxDeferredrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1falsefalsefalse00Actual after-tax returns depend on an investor's tax situation and may differ from those shown, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.falsefalsefalsexbrli:stringItemTypestringProvide a brief explanation that the actual after-tax returns depend on an investor's tax situation and may differ from those shown, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph iv -Clause B false0Performance Table Not Relevant to Tax Deferred42false 4rr_PerformanceTableOneClassOfAfterTaxShownrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1falsefalsefalse00After-tax returns are shown for Investor Class shares only; after-tax returns for other classes will vary.falsefalsefalsexbrli:stringItemTypestringProvide a brief explanation that if the Fund is a Multiple Class Fund that offers more than one Class in the prospectus, after-tax returns are shown for only one Class and after-tax returns for other Classes will vary.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph iii Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph iv -Clause C false0Performance Table One Class of after Tax Shown [Text]43false 4rr_PerformanceTableClosingTextBlockrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1falsefalsefalse00<div style="TEXT-INDENT: 36pt; DISPLAY: block; MARGIN-LEFT: 0pt; MARGIN-RIGHT: 0pt" align="justify"> <font style="DISPLAY: inline; FONT-FAMILY: Times New Roman; FONT-SIZE: 10pt">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, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.</font> </div> falsefalsefalsenonnum:textBlockItemTypenaIf the Fund has annual returns for at least one calendar year, provide a table showing the Fund's (A) average annual total return; (B) average annual total return (after taxes on distributions); and (C) average annual total return (after taxes on distributions and redemption). A Money Market Fund should show only the returns described in clause (A) of the preceding sentence. All returns should be shown for 1-, 5-, and 10- calendar year periods ending on the date of the most recently completed calendar year (or for the life of the Fund, if shorter), but only for periods subsequent to the effective date of the Fund's registration statement. The table also should show the returns of an appropriate broad-based securities market index as defined in Instruction 5 to Item 22(b)(7) for the same periods. A Fund that has been in existence for more than 10 years also may include returns for the life of the Fund. A Money Market Fund may provide the Fund's 7-day yield ending on the date of the most recent calendar year or disclose a toll-free (or collect) telephone number that investors can use to obtain the Fund's current 7-day yield. For a Fund (other than a Money Market Fund or a Fund described in General Instruction C.3.(d)(iii)), provide the information in the following table with the specified captions AVERAGE ANNUAL TOTAL RETURNS (For the periods ended December 31, _____)Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph iii false0Performance Table Closing [Text Block]44false 4rr_AverageAnnualReturnCaptionrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1falsetruefalse00 Average Annual Total Returns for the Periods Ended December 31, 2012 falsefalsefalsexbrli:stringItemTypestringThis item represents Average Anuual Total Returns. If a Multiple Class Fund offers a Class in the prospectus that converts into another Class after a stated period, compute average annual total returns in the table by using the returns of the other Class for the period after conversion.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph instructions -Clause 5 false0Caption45false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse2false truefalseS000005158Member_index_SP_500_Index_reflects_no_deduction_for_fees_expenses_or_taxesMemberhttp://www.sec.gov/CIK0000701804duration2012-12-31T00:00:002012-12-31T00:00:00falsefalseThe Merger Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldick0000701804_S000005158Memberdei_LegalEntityAxisexplicitMemberfalsefalseS&P 500 Index (reflects no deduction for fees, expenses or taxes)rr_PerformanceMeasureAxisxbrldihttp://xbrl.org/2006/xbrldick0000701804_index_SP_500_Index_reflects_no_deduction_for_fees_expenses_or_taxesMemberrr_PerformanceMeasureAxisexplicitMemberpureStandardhttp://www.xbrl.org/2003/instancepurexbrli0nanafalse0S&P 500 Index (reflects no deduction for fees, expenses or taxes)46true 3rr_RiskReturnAbstractrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Risk/Return:47false 4rr_AverageAnnualReturnLabelrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1falsetruefalse00S&P 500 Index (reflects no deduction for fees, expenses or taxes)falsefalsefalsexbrli:stringItemTypestringThis item represents Average Anuual Total Returns. If a Multiple Class Fund offers a Class in the prospectus that converts into another Class after a stated period, compute average annual total returns in the table by using the returns of the other Class for the period after conversion.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph iii -Clause 1 -Exhibit 2 false0Label48false 4rr_AverageAnnualReturnYear01rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truetruetrue0.16000.1600falsefalsefalsexbrli:pureItemTypepureReturn Before Taxes.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph iii -Clause 1 -Exhibit 2 false0Average Annual Returns, 1 Year49false 4rr_AverageAnnualReturnYear05rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truetruetrue0.01660.0166falsefalsefalsexbrli:pureItemTypepureReturn Before Taxes.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph iii -Clause 1 -Exhibit 2 false0Average Annual Returns, 5 Years50false 4rr_AverageAnnualReturnYear10rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truetruetrue0.07100.0710falsefalsefalsexbrli:pureItemTypepureReturn Before Taxes.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph iii -Clause 1 -Exhibit 2 false0Average Annual Returns, 10 Years51false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse3false USDtruefalse$S000005158Member_C000129310Memberhttp://www.sec.gov/CIK0000701804duration2012-12-31T00:00:002012-12-31T00:00:00falsefalseThe Merger Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldick0000701804_S000005158Memberdei_LegalEntityAxisexplicitMemberfalsefalseThe Merger Fund - Institutional Class Sharesrr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldick0000701804_C000129310Memberrr_ProspectusShareClassAxisexplicitMemberpureStandardhttp://www.xbrl.org/2003/instancepurexbrli0usdStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$nanafalse0The Merger Fund - Institutional Class Shares52true 3rr_RiskReturnAbstractrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Risk/Return:53false 4rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPricerr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1truetruetrue0.00000.0000falsefalsefalserr:NonNegativePure4TypepureMaximum Deferred Sales Charge (Load) (as a percentage of ____) A.3.instructions.2.a.i "Maximum Deferred Sales Charge (Load)" includes the maximum total deferred sales charge (load) payable upon redemption, in installments, or both, expressed as a percentage of the amount or amounts stated in response to Item 7(a), except that, for a sales charge (load) based on net asset value at the time of purchase, show the sales charge (load) as a percentage of the offering price at the time of purchase. A Fund may include in a footnote to the table, if applicable, a tabular presentation showing the amount of deferred sales charges (loads) over time or a narrative explanation of the sales charges (loads) (e.g., __% in the first year after purchase, declining to __% in the __ year and eliminated thereafter). A.3.instructions.2.a.ii If more than one type of sales charge (load) is imposed (e.g., a deferred sales charge (load) and a front-end sales charge (load)), the first caption in the table should read "Maximum Sales Charge (Load)" and show the maximum cumulative percentage. Show the percentage amounts and the terms of each sales charge (load) comprising that figure on separate lines below.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 1 false0Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)54false 4rr_MaximumDeferredSalesChargeOverOtherrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1truetruetrue0.00000.0000falsefalsefalserr:NonNegativePure4TypepureMaximum Deferred Sales Charge (Load) (as a percentage of ____) "Maximum Deferred Sales Charge (Load)" includes the maximum total deferred sales charge (load) payable upon redemption, in installments, or both, expressed as a percentage of the amount or amounts stated in response to Item 7(a), except that, for a sales charge (load) based on net asset value at the time of purchase, show the sales charge (load) as a percentage of the offering price at the time of purchase. A Fund may include in a footnote to the table, if applicable, a tabular presentation showing the amount of deferred sales charges (loads) over time or a narrative explanation of the sales charges (loads) (e.g., __% in the first year after purchase, declining to __% in the __ year and eliminated thereafter). If more than one type of sales charge (load) is imposed (e.g., a deferred sales charge (load) and a front-end sales charge (load)), the first caption in the table should read "Maximum Sales Charge (Load)" and show the maximum cumulative percentage. Show the percentage amounts and the terms of each sales charge (load) comprising that figure on separate lines below.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection instructions -Paragraph 2 -Subparagraph a -Clause i false0Maximum Deferred Sales Charge (Load) (as a percentage of offering price)55false 4rr_MaximumSalesChargeOnReinvestedDividendsAndDistributionsOverOtherrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1truetruetrue0.00000.0000falsefalsefalserr:NonNegativePure4TypepureMaximum Sales Charge (Load) Imposed on Reinvested Dividends[and other Distributions] (as a percentage of ____)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 3 false0Maximum Sales Charge (Load) Imposed on Reinvested Dividends and Other Distributions (as a percentage of offering price)56false 4rr_RedemptionFeeOverRedemptionrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1truetruetrue0.00000.0000falsefalsefalserr:NonPositivePure4Typepure"Redemption Fee" (as a percentage of amount redeemed, if applicable) If the Fund is an Exchange-Traded Fund and issues or redeems shares in creation units of not less than 25,000 shares each, exclude any fees charged for the purchase and redemption of the Fund's creation units. "Redemption Fee" includes a fee charged for any redemption of the Fund's shares, but does not include a deferred sales charge (load) imposed upon redemption.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection instructions -Paragraph 2 -Subparagraph b false0Redemption Fee (as a percentage of amount redeemed)57false 4rr_ExchangeFeeOverRedemptionrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1truetruetrue0.00000.0000falsefalsefalserr:NonNegativePure4TypepureExchange Fee includes the maximum fee charged for any exchange or transfer of interest from the Fund to another fund. The Fund may include in a footnote to the table, if applicable, a tabular presentation of the range of exchange fees or a narrative explanation of the fees.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection instructions -Paragraph 2 -Subparagraph c false0Exchange Fee58false 4rr_ManagementFeesOverAssetsrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1truetruetrue0.01000.0100falsefalsefalserr: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 Fees59false 4rr_DistributionAndService12b1FeesOverAssetsrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1truetruetrue0.00000.0000falsefalsefalserr:NonNegativePure4TypepureDistribution [and/or Service] (12b-1) Fees" include all distribution or other expenses incurred during the most recent fiscal year under a plan adopted pursuant to rule 12b-1 [17 CFR 270.12b-1]. Under an appropriate caption or a subcaption of "Other Expenses," disclose the amount of any distribution or similar expenses deducted from the Fund's assets other than pursuant to a rule 12b-1 plan.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 9 false0Distribution and/or Service (12b-1) Fees60false 4rr_Component1OtherExpensesOverAssetsrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1truetruetrue0.00420.0042falsefalsefalserr: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 Expenses consisting of Interest Expense, Borrowing Expense on Securities Sold Short and Dividends on Securities Sold Short61false 4rr_OtherExpensesOverAssetsrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1truetruetrue0.00580.0058falsefalsefalserr: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 false0Total Other Expenses62false 4rr_AcquiredFundFeesAndExpensesOverAssetsrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1truetruetrue0.00050.0005[1]falsefalsefalserr: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 false0Acquired Fund Fees and Expenses63false 4rr_ExpensesOverAssetsrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1truetruetrue0.01630.0163[2]falsefalsefalserr:NonNegativePure4TypepureTotal Annual Fund Operating Expenses. If the Fund is a Feeder Fund, reflect the aggregate expenses of the Feeder Fund and the Master Fund in a single fee table using the captions provided. In a footnote to the fee table, state that the table and Example reflect the expenses of both the Feeder and Master Funds. If the prospectus offers more than one Class of a Multiple Class Fund or more than one Feeder Fund that invests in the same Master Fund, provide a separate response for each Class or Feeder Fund. Base the percentages of "Annual Fund Operating Expenses" on amounts incurred during the Fund's most recent fiscal year, but include in expenses amounts that would have been incurred absent expense reimbursement or fee waiver arrangements. If the Fund has changed its fiscal year and, as a result, the most recent fiscal year is less than three months, use the fiscal year prior to the most recent fiscal year as the basis for determining "Annual Fund Operating Expenses."Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection instructions -Paragraph 3 -Subparagraph d false0Total Annual Fund Operating Expenses Before Fee Waiver64false 4rr_FeeWaiverOrReimbursementOverAssetsrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1truetruetrue-0.0013-0.0013[2]falsefalsefalserr:NonPositivePure4TypepureTotal Annual Fund Operating Expenses. If there were expense reimbursement or fee waiver arrangements that reduced any Fund operating expenses and will continue to reduce them for no less than one year from the effective date of the Fund's registration statement, a Fund may add two captions to the table one caption showing the amount of the expense reimbursement or fee waiver, and a second caption showing the Fund's net expenses after subtracting the fee reimbursement or expense waiver from the total fund operating expenses. The Fund should place these additional captions directly below the "Total Annual Fund Operating Expenses" caption of the table and should use appropriate descriptive captions, such as "Fee Waiver [and/or Expense Reimbursement]" and "Total Annual Fund Operating Expenses After Fee Waiver [and/or Expense Reimbursement]," respectively. If the Fund provides this disclosure, also disclose the period for which the expense reimbursement or fee waiver arrangement is expected to continue, and briefly describe who can terminate the arrangement and under what circumstances.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection table -Paragraph 1 -Subparagraph 11 false0Fee Waiver65false 4rr_NetExpensesOverAssetsrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1truetruetrue0.01500.0150[2]falsefalsefalserr:NonNegativePure4TypepureTotal Annual Fund Operating Expenses.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection table -Paragraph 1 -Subparagraph 11 false0Total Annual Fund Operating Expenses After Fee Waiver66false 4rr_ExpenseExampleYear01rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1truefalsetrue153153USD$falsetruefalserr:NonNegativeMonetaryTypemonetaryThe Example assumes that you invest $10,000 in the Fund for the time periods indicated and then you redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return per year and that the Fund's operating expenses remained the same. Although your actual costs may be higher or lower.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection instructions -Paragraph 4 false2Expense Example, with Redemption, 1 Year67false 4rr_ExpenseExampleYear03rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1truefalsetrue502502USD$falsefalsefalserr:NonNegativeMonetaryTypemonetaryThe Example assumes that you invest $10,000 in the Fund for the time periods indicated and then you redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return per year and that the Fund's operating expenses remained the same. Although your actual costs may be higher or lower.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection example -Paragraph 1 -Subparagraph 2 false2Expense Example, with Redemption, 3 Years68false 4rr_ExpenseExampleYear05rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1truefalsetrue874874USD$falsefalsefalserr:NonNegativeMonetaryTypemonetaryThe Example assumes that you invest $10,000 in the Fund for the time periods indicated and then you redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return per year and that the Fund's operating expenses remained the same. Although your actual costs may be higher or lower.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection example -Paragraph 1 -Subparagraph 2 false2Expense Example, with Redemption, 5 Years69false 4rr_ExpenseExampleYear10rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1truefalsetrue19221922USD$falsetruefalserr:NonNegativeMonetaryTypemonetaryThe Example assumes that you invest $10,000 in the Fund for the time periods indicated and then you redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return per year and that the Fund's operating expenses remained the same. Although your actual costs may be higher or lower.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection example -Paragraph 1 -Subparagraph 2 false2Expense Example, with Redemption, 10 Years70false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse4false truefalseS000005158Member_C000014124Memberhttp://www.sec.gov/CIK0000701804duration2012-12-31T00:00:002012-12-31T00:00:00falsefalseThe Merger Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldick0000701804_S000005158Memberdei_LegalEntityAxisexplicitMemberfalsefalseThe Merger Fund - Investor Class Sharesrr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldick0000701804_C000014124Memberrr_ProspectusShareClassAxisexplicitMemberpureStandardhttp://www.xbrl.org/2003/instancepurexbrli0nanafalse0The Merger Fund - Investor Class Shares71true 3rr_RiskReturnAbstractrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Risk/Return:72false 4rr_AnnualReturn2003rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1truetruefalse0.11040.1104falsefalsefalsexbrli:pureItemTypepureIf the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart. When a Multiple Class Fund offers more than one Class in the prospectus, provide annual total returns in the bar chart for only one of those Classes. The Fund can select which Class to include (e.g., the oldest Class, the Class with the greatest net assets).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph instructions -Clause 3 -Exhibit a false0Annual Return 200373false 4rr_AnnualReturn2004rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1truetruefalse0.02710.0271falsefalsefalsexbrli:pureItemTypepureIf the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart. When a Multiple Class Fund offers more than one Class in the prospectus, provide annual total returns in the bar chart for only one of those Classes. The Fund can select which Class to include (e.g., the oldest Class, the Class with the greatest net assets).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph instructions -Clause 3 -Exhibit a false0Annual Return 200474false 4rr_AnnualReturn2005rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1truetruefalse0.00810.0081falsefalsefalsexbrli:pureItemTypepureIf the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart. When a Multiple Class Fund offers more than one Class in the prospectus, provide annual total returns in the bar chart for only one of those Classes. The Fund can select which Class to include (e.g., the oldest Class, the Class with the greatest net assets).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph ii false0Annual Return 200575false 4rr_AnnualReturn2006rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1truetruefalse0.10980.1098falsefalsefalsexbrli:pureItemTypepureIf the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart. When a Multiple Class Fund offers more than one Class in the prospectus, provide annual total returns in the bar chart for only one of those Classes. The Fund can select which Class to include (e.g., the oldest Class, the Class with the greatest net assets).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph ii false0Annual Return 200676false 4rr_AnnualReturn2007rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1truetruefalse0.02960.0296falsefalsefalsexbrli:pureItemTypepureIf the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart. When a Multiple Class Fund offers more than one Class in the prospectus, provide annual total returns in the bar chart for only one of those Classes. The Fund can select which Class to include (e.g., the oldest Class, the Class with the greatest net assets).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph instructions -Clause 3 -Exhibit a false0Annual Return 200777false 4rr_AnnualReturn2008rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1truetruefalse-0.0226-0.0226falsefalsefalsexbrli:pureItemTypepureIf the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart. When a Multiple Class Fund offers more than one Class in the prospectus, provide annual total returns in the bar chart for only one of those Classes. The Fund can select which Class to include (e.g., the oldest Class, the Class with the greatest net assets).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph ii false0Annual Return 200878false 4rr_AnnualReturn2009rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1truetruefalse0.08520.0852falsefalsefalsexbrli:pureItemTypepureIf the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart. When a Multiple Class Fund offers more than one Class in the prospectus, provide annual total returns in the bar chart for only one of those Classes. The Fund can select which Class to include (e.g., the oldest Class, the Class with the greatest net assets).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph instructions -Clause 3 -Exhibit a false0Annual Return 200979false 4rr_AnnualReturn2010rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1truetruefalse0.03410.0341falsefalsefalsexbrli:pureItemTypepureIf the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart. When a Multiple Class Fund offers more than one Class in the prospectus, provide annual total returns in the bar chart for only one of those Classes. The Fund can select which Class to include (e.g., the oldest Class, the Class with the greatest net assets).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph ii false0Annual Return 201080false 4rr_AnnualReturn2011rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1truetruefalse0.01660.0166falsefalsefalsexbrli:pureItemTypepureIf the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart. When a Multiple Class Fund offers more than one Class in the prospectus, provide annual total returns in the bar chart for only one of those Classes. The Fund can select which Class to include (e.g., the oldest Class, the Class with the greatest net assets).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph instructions -Clause 3 -Exhibit a false0Annual Return 201181false 4rr_AnnualReturn2012rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1truetruefalse0.03610.0361falsefalsefalsexbrli:pureItemTypepureIf the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart. When a Multiple Class Fund offers more than one Class in the prospectus, provide annual total returns in the bar chart for only one of those Classes. The Fund can select which Class to include (e.g., the oldest Class, the Class with the greatest net assets).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph ii false0Annual Return 201282false 4rr_AverageAnnualReturnLabelrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1falsetruefalse00 Investor Class Shares - Return Before Taxesfalsefalsefalsexbrli:stringItemTypestringThis item represents Average Anuual Total Returns. If a Multiple Class Fund offers a Class in the prospectus that converts into another Class after a stated period, compute average annual total returns in the table by using the returns of the other Class for the period after conversion.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph iii -Clause 1 -Exhibit 2 false0Label83false 4rr_AverageAnnualReturnYear01rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truetruetrue0.03610.0361[3]falsefalsefalsexbrli:pureItemTypepureReturn Before Taxes.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph iii -Clause 1 -Exhibit 2 false0Average Annual Returns, 1 Year84false 4rr_AverageAnnualReturnYear05rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truetruetrue0.02930.0293[3]falsefalsefalsexbrli:pureItemTypepureReturn Before Taxes.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph iii -Clause 1 -Exhibit 2 false0Average Annual Returns, 5 Years85false 4rr_AverageAnnualReturnYear10rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truetruetrue0.04260.0426[3]falsefalsefalsexbrli:pureItemTypepureReturn Before Taxes.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph iii -Clause 1 -Exhibit 2 false0Average Annual Returns, 10 Years86false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse5false truefalseS000005158Member_AfterTaxesOnDistributionsMember_C000014124Memberhttp://www.sec.gov/CIK0000701804duration2012-12-31T00:00:002012-12-31T00:00:00falsefalseThe Merger Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldick0000701804_S000005158Memberdei_LegalEntityAxisexplicitMemberfalsefalseThe Merger Fund - Investor Class Sharesrr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldick0000701804_C000014124Memberrr_ProspectusShareClassAxisexplicitMemberfalsefalseAfter Taxes on Distributionsrr_PerformanceMeasureAxisxbrldihttp://xbrl.org/2006/xbrldirr_AfterTaxesOnDistributionsMemberrr_PerformanceMeasureAxisexplicitMemberpureStandardhttp://www.xbrl.org/2003/instancepurexbrli0nanafalse0The Merger Fund - Investor Class Shares | After Taxes on Distributions87true 3rr_RiskReturnAbstractrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Risk/Return:88false 4rr_AverageAnnualReturnLabelrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1falsetruefalse00 Investor Class Shares - Return After Taxes on Distributionsfalsefalsefalsexbrli:stringItemTypestringThis item represents Average Anuual Total Returns. If a Multiple Class Fund offers a Class in the prospectus that converts into another Class after a stated period, compute average annual total returns in the table by using the returns of the other Class for the period after conversion.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph iii -Clause 1 -Exhibit 2 false0Label89false 4rr_AverageAnnualReturnYear01rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truetruetrue0.03120.0312[3]falsefalsefalsexbrli:pureItemTypepureReturn Before Taxes.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph iii -Clause 1 -Exhibit 2 false0Average Annual Returns, 1 Year90false 4rr_AverageAnnualReturnYear05rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truetruetrue0.02400.0240[3]falsefalsefalsexbrli:pureItemTypepureReturn Before Taxes.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph iii -Clause 1 -Exhibit 2 false0Average Annual Returns, 5 Years91false 4rr_AverageAnnualReturnYear10rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truetruetrue0.03430.0343[3]falsefalsefalsexbrli:pureItemTypepureReturn Before Taxes.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph iii -Clause 1 -Exhibit 2 false0Average Annual Returns, 10 Years92false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse6false truefalseS000005158Member_AfterTaxesOnDistributionsAndSalesMember_C000014124Memberhttp://www.sec.gov/CIK0000701804duration2012-12-31T00:00:002012-12-31T00:00:00falsefalseThe Merger Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldick0000701804_S000005158Memberdei_LegalEntityAxisexplicitMemberfalsefalseThe Merger Fund - Investor Class Sharesrr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldick0000701804_C000014124Memberrr_ProspectusShareClassAxisexplicitMemberfalsefalseAfter Taxes on Distributions and Sale of Fund Sharesrr_PerformanceMeasureAxisxbrldihttp://xbrl.org/2006/xbrldirr_AfterTaxesOnDistributionsAndSalesMemberrr_PerformanceMeasureAxisexplicitMemberpureStandardhttp://www.xbrl.org/2003/instancepurexbrli0nanafalse0The Merger Fund - Investor Class Shares | After Taxes on Distributions and Sale of Fund Shares93true 3rr_RiskReturnAbstractrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Risk/Return:94false 4rr_AverageAnnualReturnLabelrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalselabel1falsetruefalse00 Investor Class Shares - Return After Taxes on Distributions and Sale of Fund Sharesfalsefalsefalsexbrli:stringItemTypestringThis item represents Average Anuual Total Returns. If a Multiple Class Fund offers a Class in the prospectus that converts into another Class after a stated period, compute average annual total returns in the table by using the returns of the other Class for the period after conversion.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph iii -Clause 1 -Exhibit 2 false0Label95false 4rr_AverageAnnualReturnYear01rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truetruetrue0.02580.0258[3]falsefalsefalsexbrli:pureItemTypepureReturn Before Taxes.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph iii -Clause 1 -Exhibit 2 false0Average Annual Returns, 1 Year96false 4rr_AverageAnnualReturnYear05rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truetruetrue0.02240.0224[3]falsefalsefalsexbrli:pureItemTypepureReturn Before Taxes.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph iii -Clause 1 -Exhibit 2 false0Average Annual Returns, 5 Years97false 4rr_AverageAnnualReturnYear10rr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truetruetrue0.03250.0325[3]falsefalsefalsexbrli:pureItemTypepureReturn Before Taxes.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection b -Paragraph 2 -Subparagraph iii -Clause 1 -Exhibit 2 false0Average Annual Returns, 10 Years1Acquired Fund Fees and Expenses are the indirect costs of investing in other investment companies. The operating expenses in this fee table may not correlate to the expense ratio in the Fund's financial highlights because the financial statements include only the direct operating expenses incurred by the Fund, not the indirect costs of investing in other investment companies.2The Fund's contractual management fee rate is 1.00% of the Fund's average net assets. The Adviser has agreed to reduce its management fee until July 8, 2014 so that the management fee will be: (i) 1.0% on an annualized basis of the average daily net assets of the Fund on net assets below $1.5 billion; (ii) 0.9% on an annualized basis of the average daily net assets of the Fund on net assets between $1.5 billion and $2.0 billion; (iii) 0.8% on an annualized basis of the average daily net assets of the Fund on net assets between $2.0 billion and $5.0 billion and (iv) 0.75% on an annualized basis of the average daily net assets of the Fund on net assets over $5.0 billion. This fee waiver arrangement may be terminated at any time by the Fund's Board of Trustees.3The returns are for Investor Class shares of the Fund, which are not offered in this Prospectus. Institutional Class shares represent an investment in the same portfolio of securities as Investor Class shares. Average Annual Total Returns would differ only to the extent that Institutional Class shares do not have the same expenses as Investor Class shares.falseRisk/Return Detail Data - The Merger Fund (The Merger Fund, USD $)NoRoundingUnKnownUnKnownUnKnowntruefalsefalseSheethttp://usbank.com/20130708/role/DisclosureRiskReturnDetailDataElementsTheMergerFund197