rr_DistributionAndService12b1FeesOverAssets

none

^[1]

rr_OtherExpensesOverAssets

0.17%

rr_FeeWaiverOrReimbursementOverAssets

none

^[2]

rr_ExpenseExampleNoRedemptionYear01

$ 72

rr_ExpenseExampleNoRedemptionYear05

499

rr_AnnualReturn2008

(42.87%)

rr_AnnualReturn2010

31.98%

rr_AnnualReturn2012

15.82%

rr_AverageAnnualReturnYear01

42.99%

rr_AverageAnnualReturnSinceInception

8.19%

rr_AverageAnnualReturnYear01

42.75%

rr_AverageAnnualReturnSinceInception

7.92%

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear05

23.35%

rr_AverageAnnualReturnLabel

(reflects no deduction for fees, expenses or taxes)

rr_AverageAnnualReturnYear05

29.22%

rr_AverageAnnualReturnLabel

(reflects no deduction for fees, expenses or taxes)

rr_AverageAnnualReturnYear05

18.59%

rr_AverageAnnualReturnLabel

(reflects no deduction for fees, expenses or taxes)

rr_AverageAnnualReturnYear05

27.69%

rr_AverageAnnualReturnLabel

(reflects no deduction for fees, expenses or taxes)

rr_AverageAnnualReturnYear05

27.01%

rr_RiskReturnHeading

SUMMARY INFORMATION

rr_ObjectivePrimaryTextBlock

The First Trust Consumer Staples AlphaDEX(R) Fund (the "Fund") seeks investment results that correspond generally to the price and yield (before the Fund's fees and expenses) of an equity index called the StrataQuant(R) Consumer Staples Index (the "Index").

rr_ExpenseNarrativeTextBlock

The following table describes the fees and expenses you may pay if you buy and hold shares of the Fund. Investors purchasing and selling shares may be subject to costs (including customary brokerage commissions) charged by their broker, which are not reflected in the table below.

rr_OperatingExpensesCaption

ANNUAL FUND OPERATING EXPENSES (expenses that you pay each year as a percentage of the value of your investment)

Expense Example, No Redemption Narrative [Text Block]

rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 100% of the average value of its portfolio.

rr_ExpenseExampleNoRedemptionNarrativeTextBlock

The example below is intended to help you compare the cost of investing in the Fund with the cost of investing in other funds. This example does not take into account customary brokerage commissions that you pay when purchasing or selling shares of the Fund in the secondary market.

The example assumes that you invest $10,000 in the Fund for the time periods indicated. The example also assumes that your investment has a 5% return each year and that the Fund's operating expenses remain at current levels. Additionally, the example assumes that the Fund imposes a 12b-1 fee of 0.25% per annum of the Fund's average daily net assets following December 31, 2015. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

rr_StrategyNarrativeTextBlock

The Fund will normally invest at least 90% (plus the amount of any borrowings for investment purposes) of its net assets in common stocks that comprise the Index. The Fund, using an "indexing" investment approach, attempts to replicate, before fees and expenses, the performance of the Index. First Trust seeks a correlation of 0.95 or better (before fees and expenses) between the Fund's performance and the performance of the Index; a figure of 1.00 would represent perfect correlation.

The Index is in the "StrataQuant(R) Series," a family of custom enhanced indices developed, maintained and sponsored by NYSE Group, Inc. or its affiliates ("NYSE" or an "Index Provider"), and licensed to First Trust Portfolios L.P. by NYSE. Prior to the acquisition of the American Stock Exchange LLC (the "AMEX") by NYSE, the equity indices in the StrataQuant(R) Series were developed, maintained and sponsored by the AMEX. The Index is a modified equal-dollar weighted index designed by NYSE to objectively identify and select stocks from the Russell 1000(R) Index in the consumer staples sector that may generate positive alpha relative to traditional passive-style indices through the use of the AlphaDEX(R) selection methodology. Alpha is an indication of how much an investment outperforms or underperforms on a risk-adjusted basis relative to its benchmark. As of July 31, 2014, the Index was comprised of 38 stocks. The Index is rebalanced and reconstituted as of the last business day of each calendar quarter. Changes to the Index will be effective at the open of trading on the fourth business day of the following month.

rr_RiskNarrativeTextBlock

You could lose money by investing in the Fund. An investment in the Fund is not a deposit of a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency. There can be no assurance that the Fund's investment objective will be achieved.

CONSUMER STAPLES COMPANIES RISK. The Fund invests in the securities of consumer staples companies, which provide products directly to the consumer that are typically considered non-discretionary items based on consumer purchasing habits. The success of these companies is affected by a variety of factors, such as government regulations, which may affect the permissibility of using various food additives and the production methods of companies that manufacture food products.

EQUITY SECURITIES RISK. Because the Fund invests in equity securities, the value of the Fund's shares will fluctuate with changes in the value of these equity securities. Equity securities prices fluctuate for several reasons, including changes in investors' perceptions of the financial condition of an issuer or the general condition of the relevant stock market, such as the current market volatility, or when political or economic events affecting the issuers occur. In addition, common stock prices may be particularly sensitive to rising interest rates, as the cost of capital rises and borrowing costs increase.

INDEX CORRELATION RISK. You should anticipate that the value of Fund shares will decline more or less in correlation with any decline in the value of the Fund's Index.

MARKET RISK. Market risk is the risk that the underlying securities in which the Fund invests, or shares of the Fund in general, may fall in value. Securities are subject to market fluctuations caused by such factors as economic, political, regulatory or market developments, changes in interest rates and perceived trends in securities prices. Overall securities values could decline generally or could underperform other investments.

NON-CORRELATION RISK. The Fund's return may not match the return of the Index for a number of reasons. For example, the Fund incurs operating expenses not applicable to the Index, and may incur costs in buying and selling securities, especially when rebalancing the Fund's portfolio holdings to reflect changes in the composition of the Index. In addition, the Fund's portfolio holdings may not exactly replicate the securities included in the Index or the ratios between the securities included in the Index.

REPLICATION MANAGEMENT RISK. The Fund is exposed to additional market risk due to its policy of investing principally in the securities included in the Index. As a result of this policy, securities held by the Fund will generally not be bought or sold in response to market fluctuations, and the securities may be issued by companies concentrated in a particular industry if the Index is so concentrated. Therefore, the Fund will generally not sell a security because its issuer is in financial trouble, unless that security is removed or is anticipated to be removed from the Index.

SMALLER COMPANIES RISK. The Fund may invest in small and/or mid-capitalization companies. Such companies may be more vulnerable to adverse general market or economic developments, and their securities may be less liquid and may experience greater price volatility than larger, more established companies as a result of several factors, including limited trading volumes, products or financial resources, management inexperience and less publicly available information. Accordingly, such companies are generally subject to greater market risk than larger, more established companies.

rr_PerformanceNarrativeTextBlock

The bar chart and table below illustrate the annual calendar year returns of the Fund based on net asset value for the past six years as well as the average annual Fund and Index returns for the one year, five year and since inception periods ended December 31, 2013. The bar chart and table provide an 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 total returns based on net asset value compare to those of the Index, a broad-based market index and two specialized securities market indices. With respect to the Russell 1000(R) Consumer Staples Index, on or about September 18, 2008, Russell Investment Group ("Russell") began calculating its Russell U.S. Indices using an enhanced Russell sector scheme, the Russell Global Sectors (the "RGS"). The RGS and the former U.S. sector scheme ran in tandem until June 30, 2009, when Russell officially transitioned to the RGS and ceased calculating its indices using the U.S. sector scheme. Consequently, performance data is not available for the Russell 1000(R) Consumer Staples Index for the entire "5 Years" or "Since Inception" periods set forth in the table because performance data does not exist using solely the U.S. sector scheme or alternatively, using solely the RGS. See "Total Return Information" for additional performance information regarding the Fund. The Fund's performance information is accessible on the Fund's website at www.ftportfolios.com.

Returns before taxes do not reflect the effects of any income or capital gains taxes. All after-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of any state or local tax. Returns after taxes on distributions reflect the taxed return on the payment of dividends and capital gains. Returns after taxes on distributions and sale of shares assume you sold your shares at period end, and, therefore, are also adjusted for any capital gains or losses incurred. Returns for the market indices do not include expenses, which are deducted from Fund returns, or taxes.

Your own actual after-tax returns will depend on your specific tax situation and may differ from what is shown here. After-tax returns are not relevant to investors who hold Fund shares in tax-deferred accounts such as individual retirement accounts (IRAs) or employee-sponsored retirement plans.

rr_BarChartFootnotesTextBlock

(1) The Fund's year-to-date return based on net asset value for the period 12/31/2013 to 9/30/2014 was 10.72%.

rr_PerformanceTableHeading

AVERAGE ANNUAL TOTAL RETURNS FOR THE PERIODS ENDED DECEMBER 31, 2013

rr_RiskReturnAbstract

Fees Previously Waived or Expenses Reimbursed by First Trust

rr_ManagementFeesOverAssets

0.50%

rr_Component1OtherExpensesOverAssets

none

^[2],[3]

Total Net Annual Fund Operating Expenses After Fee Waiver and Expense Reimbursement

rr_ExpensesOverAssets

0.67%

rr_NetExpensesOverAssets

0.67%

rr_ExpenseExampleNoRedemptionYear03

266

rr_ExpenseExampleNoRedemptionYear10

1,106

rr_AnnualReturn2009

27.13%

rr_AnnualReturn2011

13.15%

rr_AnnualReturn2013

41.94%

rr_AverageAnnualReturnYear05

21.76%

rr_AverageAnnualReturnInceptionDate

May 08, 2007

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear05

21.23%

rr_AverageAnnualReturnYear01

23.71%

rr_AverageAnnualReturnSinceInception

8.13%

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear01

43.09%

rr_AverageAnnualReturnSinceInception

11.31%

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear01

33.11%

rr_AverageAnnualReturnSinceInception

5.66%

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear01

26.14%

rr_AverageAnnualReturnSinceInception

10.27%

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear01

27.68%

rr_AverageAnnualReturnSinceInception

rr_RiskReturnAbstract

rr_ObjectiveHeading

INVESTMENT OBJECTIVE

rr_ExpenseHeading

FEES AND EXPENSES OF THE FUND

rr_ShareholderFeesCaption

SHAREHOLDER FEES (fees paid directly from your investment)

rr_PortfolioTurnoverHeading

PORTFOLIO TURNOVER

rr_ExpenseExampleHeading

EXAMPLE

rr_StrategyHeading

PRINCIPAL INVESTMENT STRATEGIES

rr_RiskHeading

PRINCIPAL RISKS

rr_BarChartAndPerformanceTableHeading

ANNUAL TOTAL RETURN

rr_BarChartHeading

FIRST TRUST ENERGY ALPHADEX(R) FUND--TOTAL RETURNS(1)

Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)

rr_BarChartClosingTextBlock

During the six-year period ended December 31, 2013, the Fund's highest and lowest calendar quarter returns were 29.92% and -38.75%, respectively, for the quarters ended June 30, 2008 and December 31, 2008. The Fund's past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future.

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

rr_DistributionAndService12b1FeesOverAssets

none

^[1]

rr_OtherExpensesOverAssets

0.17%

rr_FeeWaiverOrReimbursementOverAssets

none

^[2]

rr_ExpenseExampleNoRedemptionYear01

68

rr_ExpenseExampleNoRedemptionYear05

483

rr_AnnualReturn2008

(50.78%)

rr_AnnualReturn2010

27.77%

rr_AnnualReturn2012

3.67%

rr_AverageAnnualReturnYear01

28.66%

rr_AverageAnnualReturnSinceInception

4.20%

rr_AverageAnnualReturnYear01

28.16%

rr_AverageAnnualReturnSinceInception

3.97%

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear05

14.68%

rr_AverageAnnualReturnLabel

(reflects no deduction for fees, expenses or taxes)

rr_AverageAnnualReturnYear05

19.10%

rr_AverageAnnualReturnLabel

(reflects no deduction for fees, expenses or taxes)

rr_AverageAnnualReturnYear05

18.59%

rr_AverageAnnualReturnLabel

(reflects no deduction for fees, expenses or taxes)

rr_AverageAnnualReturnYear05

13.44%

rr_AverageAnnualReturnLabel

(reflects no deduction for fees, expenses or taxes)

rr_AverageAnnualReturnYear05

13.88%

rr_RiskReturnHeading

SUMMARY INFORMATION

rr_ObjectivePrimaryTextBlock

The First Trust Financials AlphaDEX(R) Fund (the "Fund") seeks investment results that correspond generally to the price and yield (before the Fund's fees and expenses) of an equity index called the StrataQuant(R) Financials Index (the "Index").

rr_ExpenseNarrativeTextBlock

The following table describes the fees and expenses you may pay if you buy and hold shares of the Fund. Investors purchasing and selling shares may be subject to costs (including customary brokerage commissions) charged by their broker, which are not reflected in the table below.

rr_OperatingExpensesCaption

ANNUAL FUND OPERATING EXPENSES (expenses that you pay each year as a percentage of the value of your investment)

Expense Example, No Redemption Narrative [Text Block]

rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 55% of the average value of its portfolio.

rr_ExpenseExampleNoRedemptionNarrativeTextBlock

The example below is intended to help you compare the cost of investing in the Fund with the cost of investing in other funds. This example does not take into account customary brokerage commissions that you pay when purchasing or selling shares of the Fund in the secondary market.

The example assumes that you invest $10,000 in the Fund for the time periods indicated. The example also assumes that your investment has a 5% return each year and that the Fund's operating expenses remain at current levels. Additionally, the example assumes that the Fund imposes a 12b-1 fee of 0.25% per annum of the Fund's average daily net assets following December 31, 2015. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

rr_StrategyNarrativeTextBlock

The Fund will normally invest at least 90% (plus the amount of any borrowings for investment purposes) of its net assets in common stocks that comprise the Index. The Fund, using an "indexing" investment approach, attempts to replicate, before fees and expenses, the performance of the Index. First Trust seeks a correlation of 0.95 or better (before fees and expenses) between the Fund's performance and the performance of the Index; a figure of 1.00 would represent perfect correlation.

The Index is in the "StrataQuant(R) Series," a family of custom enhanced indices developed, maintained and sponsored by NYSE Group, Inc. or its affiliates ("NYSE" or an "Index Provider"), and licensed to First Trust Portfolios L.P. by NYSE. Prior to the acquisition of the American Stock Exchange LLC (the "AMEX") by NYSE, the equity indices in the StrataQuant(R) Series were developed, maintained and sponsored by the AMEX. The Index is a modified equal-dollar weighted index designed by NYSE to objectively identify and select stocks from the Russell 1000(R) Index in the financial services sector that may generate positive alpha relative to traditional passive-style indices through the use of the AlphaDEX(R) selection methodology. Alpha is an indication of how much an investment outperforms or underperforms on a risk-adjusted basis relative to its benchmark. The Fund may invest in common stocks and business development companies ("BDCs") that comprise the Index. As of July 31, 2014, the Index was comprised of 171 stocks. The Index is rebalanced and reconstituted as of the last business day of each calendar quarter. Changes to the Index will be effective at the open of trading on the fourth business day of the following month.

rr_RiskNarrativeTextBlock

You could lose money by investing in the Fund. An investment in the Fund is not a deposit of a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency. There can be no assurance that the Fund's investment objective will be achieved.

BDC RISK. The Fund may invest in BDCs which may carry risks similar to those of a private equity or venture capital fund. BDCs are not redeemable at the option of the shareholder and they may trade in the market at a discount to their net asset value. The BDCs held by the Fund may employ the use of leverage through borrowings or the issuance of preferred stock. While leverage often serves to increase the yield of a BDC, this leverage also subjects a BDC to increased risks, including the likelihood of increased volatility and the possibility that a BDC's common share income will fall if the dividend rate of the preferred shares or the interest rate on any borrowings rises.

EQUITY SECURITIES RISK. Because the Fund invests in equity securities, the value of the Fund's shares will fluctuate with changes in the value of these equity securities. Equity securities prices fluctuate for several reasons, including changes in investors' perceptions of the financial condition of an issuer or the general condition of the relevant stock market, such as the current market volatility, or when political or economic events affecting the issuers occur. In addition, common stock prices may be particularly sensitive to rising interest rates, as the cost of capital rises and borrowing costs increase.

FINANCIAL COMPANIES RISK. Financial companies are especially subject to the adverse effects of economic recession, currency exchange rates, government regulation, decreases in the availability of capital, volatile interest rates, portfolio concentrations in geographic markets and in commercial and residential real estate loans, and competition from new entrants in their fields of business.

INDEX CORRELATION RISK. You should anticipate that the value of Fund shares will decline more or less in correlation with any decline in the value of the Fund's Index.

MARKET RISK. Market risk is the risk that the underlying securities in which the Fund invests, or shares of the Fund in general, may fall in value. Securities are subject to market fluctuations caused by such factors as economic, political, regulatory or market developments, changes in interest rates and perceived trends in securities prices. Overall securities values could decline generally or could underperform other investments.

NON-CORRELATION RISK. The Fund's return may not match the return of the Index for a number of reasons. For example, the Fund incurs operating expenses not applicable to the Index, and may incur costs in buying and selling securities, especially when rebalancing the Fund's portfolio holdings to reflect changes in the composition of the Index. In addition, the Fund's portfolio holdings may not exactly replicate the securities included in the Index or the ratios between the securities included in the Index.

REPLICATION MANAGEMENT RISK. The Fund is exposed to additional market risk due to its policy of investing principally in the securities included in the Index. As a result of this policy, securities held by the Fund will generally not be bought or sold in response to market fluctuations, and the securities may be issued by companies concentrated in a particular industry if the Index is so concentrated. Therefore, the Fund will generally not sell a security because its issuer is in financial trouble, unless that security is removed or is anticipated to be removed from the Index.

SMALLER COMPANIES RISK. The Fund may invest in small and/or mid-capitalization companies. Such companies may be more vulnerable to adverse general market or economic developments, and their securities may be less liquid and may experience greater price volatility than larger, more established companies as a result of several factors, including limited trading volumes, products or financial resources, management inexperience and less publicly available information. Accordingly, such companies are generally subject to greater market risk than larger, more established companies.

rr_PerformanceNarrativeTextBlock

The bar chart and table below illustrate the annual calendar year returns of the Fund based on net asset value for the past six years as well as the average annual Fund and Index returns for the one year, five year and since inception periods ended December 31, 2013. The bar chart and table provide an 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 total returns based on net asset value compare to those of the Index, a broad-based market index and two specialized securities market indices. With respect to the Russell 1000(R) Financial Services Index, on or about September 18, 2008, Russell Investment Group ("Russell") began calculating its Russell U.S. Indices using an enhanced Russell sector scheme, the Russell Global Sectors (the "RGS"). The RGS and the former U.S. sector scheme ran in tandem until June 30, 2009, when Russell officially transitioned to the RGS and ceased calculating its indices using the U.S. sector scheme. Consequently, performance data is not available for the Russell 1000(R) Financial Services Index for the entire "5 Years" or "Since Inception" periods set forth in the table because performance data does not exist using solely the U.S. sector scheme or alternatively, using solely the RGS. See "Total Return Information" for additional performance information regarding the Fund. The Fund's performance information is accessible on the Fund's website at www.ftportfolios.com.

Returns before taxes do not reflect the effects of any income or capital gains taxes. All after-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of any state or local tax. Returns after taxes on distributions reflect the taxed return on the payment of dividends and capital gains. Returns after taxes on distributions and sale of shares assume you sold your shares at period end, and, therefore, are also adjusted for any capital gains or losses incurred. Returns for the market indices do not include expenses, which are deducted from Fund returns, or taxes.

Your own actual after-tax returns will depend on your specific tax situation and may differ from what is shown here. After-tax returns are not relevant to investors who hold Fund shares in tax-deferred accounts such as individual retirement accounts (IRAs) or employee-sponsored retirement plans.

rr_BarChartFootnotesTextBlock

(1) The Fund's year-to-date return based on net asset value for the period 12/31/2013 to 9/30/2014 was 1.56%.

rr_PerformanceTableHeading

AVERAGE ANNUAL TOTAL RETURNS FOR THE PERIODS ENDED DECEMBER 31, 2013

rr_RiskReturnAbstract

Fees Previously Waived or Expenses Reimbursed by First Trust

rr_ManagementFeesOverAssets

0.50%

rr_Component1OtherExpensesOverAssets

none

^[2],[3]

Acquired Fund Fees and Expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.13%

^[4]

rr_FeeWaiverOrReimbursementOverAssets

none

^[2]

rr_ExpenseExampleNoRedemptionYear01

82

rr_ExpenseExampleNoRedemptionYear05

553

rr_AnnualReturn2008

(38.24%)

rr_AnnualReturn2010

19.11%

rr_AnnualReturn2012

21.24%

rr_AverageAnnualReturnYear01

40.41%

rr_AverageAnnualReturnSinceInception

3.03%

rr_AverageAnnualReturnYear01

39.60%

rr_AverageAnnualReturnSinceInception

2.39%

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear05

15.84%

rr_AverageAnnualReturnLabel

(reflects no deduction for fees, expenses or taxes)

rr_AverageAnnualReturnYear05

20.93%

rr_AverageAnnualReturnLabel

(reflects no deduction for fees, expenses or taxes)

rr_AverageAnnualReturnYear05

18.59%

rr_AverageAnnualReturnLabel

(reflects no deduction for fees, expenses or taxes)

rr_AverageAnnualReturnYear05

13.75%

rr_AverageAnnualReturnLabel

(reflects no deduction for fees, expenses or taxes)

rr_AverageAnnualReturnYear05

14.91%

rr_RiskReturnHeading

SUMMARY INFORMATION

rr_ObjectivePrimaryTextBlock

The First Trust Health Care AlphaDEX(R) Fund (the "Fund") seeks investment results that correspond generally to the price and yield (before the Fund's fees and expenses) of an equity index called the StrataQuant(R) Health Care Index (the "Index").

rr_ExpenseNarrativeTextBlock

The following table describes the fees and expenses you may pay if you buy and hold shares of the Fund. Investors purchasing and selling shares may be subject to costs (including customary brokerage commissions) charged by their broker, which are not reflected in the table below.

rr_OperatingExpensesCaption

ANNUAL FUND OPERATING EXPENSES (expenses that you pay each year as a percentage of the value of your investment)

Expense Example, No Redemption Narrative [Text Block]

rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 81% of the average value of its portfolio.

rr_ExpenseExampleNoRedemptionNarrativeTextBlock

The example below is intended to help you compare the cost of investing in the Fund with the cost of investing in other funds. This example does not take into account customary brokerage commissions that you pay when purchasing or selling shares of the Fund in the secondary market.

The example assumes that you invest $10,000 in the Fund for the time periods indicated. The example also assumes that your investment has a 5% return each year and that the Fund's operating expenses remain at current levels. Additionally, the example assumes that the Fund imposes a 12b-1 fee of 0.25% per annum of the Fund's average daily net assets following December 31, 2015. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

rr_StrategyNarrativeTextBlock

The Fund will normally invest at least 90% (plus the amount of any borrowings for investment purposes) of its net assets in common stocks that comprise the Index. The Fund, using an "indexing" investment approach, attempts to replicate, before fees and expenses, the performance of the Index. First Trust seeks a correlation of 0.95 or better (before fees and expenses) between the Fund's performance and the performance of the Index; a figure of 1.00 would represent perfect correlation.

The Index is in the "StrataQuant(R) Series," a family of custom enhanced indices developed, maintained and sponsored by NYSE Group, Inc. or its affiliates ("NYSE" or an "Index Provider"), and licensed to First Trust Portfolios L.P. by NYSE. Prior to the acquisition of the American Stock Exchange LLC (the "AMEX") by NYSE, the equity indices in the StrataQuant(R) Series were developed, maintained and sponsored by the AMEX. The Index is a modified equal-dollar weighted index designed by NYSE to objectively identify and select stocks from the Russell 1000(R) Index in the health care sector that may generate positive alpha relative to traditional passive-style indices through the use of the AlphaDEX(R) selection methodology. Alpha is an indication of how much an investment outperforms or underperforms on a risk-adjusted basis relative to its benchmark. As of July 31, 2014, the Index was comprised of 76 stocks. The Index is rebalanced and reconstituted as of the last business day of each calendar quarter. Changes to the Index will be effective at the open of trading on the fourth business day of the following month.

rr_RiskNarrativeTextBlock

You could lose money by investing in the Fund. An investment in the Fund is not a deposit of a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency. There can be no assurance that the Fund's investment objective will be achieved.

EQUITY SECURITIES RISK. Because the Fund invests in equity securities, the value of the Fund's shares will fluctuate with changes in the value of these equity securities. Equity securities prices fluctuate for several reasons, including changes in investors' perceptions of the financial condition of an issuer or the general condition of the relevant stock market, such as the current market volatility, or when political or economic events affecting the issuers occur. In addition, common stock prices may be particularly sensitive to rising interest rates, as the cost of capital rises and borrowing costs increase.

HEALTH CARE COMPANIES RISK. The Fund invests in the securities of health care companies, which are companies involved in medical services or health care, including biotechnology research and production, drugs and pharmaceuticals and health care facilities and services. These companies are subject to extensive competition, generic drug sales or the loss of patent protection, product liability litigation and increased government regulation. Research and development costs of bringing new drugs to market are substantial, and there is no guarantee that the product will ever come to market. Health care facility operators may be affected by the demand for services, efforts by government or insurers to limit rates, restriction of government financial assistance and competition from other providers.

INDEX CORRELATION RISK. You should anticipate that the value of Fund shares will decline more or less in correlation with any decline in the value of the Fund's Index.

MARKET RISK. Market risk is the risk that the underlying securities in which the Fund invests, or shares of the Fund in general, may fall in value. Securities are subject to market fluctuations caused by such factors as economic, political, regulatory or market developments, changes in interest rates and perceived trends in securities prices. Overall securities values could decline generally or could underperform other investments.

NON-CORRELATION RISK. The Fund's return may not match the return of the Index for a number of reasons. For example, the Fund incurs operating expenses not applicable to the Index, and may incur costs in buying and selling securities, especially when rebalancing the Fund's portfolio holdings to reflect changes in the composition of the Index. In addition, the Fund's portfolio holdings may not exactly replicate the securities included in the Index or the ratios between the securities included in the Index.

REPLICATION MANAGEMENT RISK. The Fund is exposed to additional market risk due to its policy of investing principally in the securities included in the Index. As a result of this policy, securities held by the Fund will generally not be bought or sold in response to market fluctuations, and the securities may be issued by companies concentrated in a particular industry if the Index is so concentrated. Therefore, the Fund will generally not sell a security because its issuer is in financial trouble, unless that security is removed or is anticipated to be removed from the Index.

SMALLER COMPANIES RISK. The Fund may invest in small and/or mid-capitalization companies. Such companies may be more vulnerable to adverse general market or economic developments, and their securities may be less liquid and may experience greater price volatility than larger, more established companies as a result of several factors, including limited trading volumes, products or financial resources, management inexperience and less publicly available information. Accordingly, such companies are generally subject to greater market risk than larger, more established companies.

rr_PerformanceNarrativeTextBlock

The bar chart and table below illustrate the annual calendar year returns of the Fund based on net asset value for the past six years as well as the average annual Fund and Index returns for the one year, five year and since inception periods ended December 31, 2013. The bar chart and table provide an 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 total returns based on net asset value compare to those of the Index, a broad-based market index and two specialized securities market indices. With respect to the Russell 1000(R) Health Care Index, on or about September 18, 2008, Russell Investment Group ("Russell") began calculating its Russell U.S. Indices using an enhanced Russell sector scheme, the Russell Global Sectors (the "RGS"). The RGS and the former U.S. sector scheme ran in tandem until June 30, 2009, when Russell officially transitioned to the RGS and ceased calculating its indices using the U.S. sector scheme. Consequently, performance data is not available for the Russell 1000(R) Health Care Index for the entire "5 Years" or "Since Inception" periods set forth in the table because performance data does not exist using solely the U.S. sector scheme or alternatively, using solely the RGS. See "Total Return Information" for additional performance information regarding the Fund. The Fund's performance information is accessible on the Fund's website at www.ftportfolios.com.

Returns before taxes do not reflect the effects of any income or capital gains taxes. All after-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of any state or local tax. Returns after taxes on distributions reflect the taxed return on the payment of dividends and capital gains. Returns after taxes on distributions and sale of shares assume you sold your shares at period end, and, therefore, are also adjusted for any capital gains or losses incurred. Returns for the market indices do not include expenses, which are deducted from Fund returns, or taxes.

Your own actual after-tax returns will depend on your specific tax situation and may differ from what is shown here. After-tax returns are not relevant to investors who hold Fund shares in tax-deferred accounts such as individual retirement accounts (IRAs) or employee-sponsored retirement plans.

rr_BarChartFootnotesTextBlock

(1) The Fund's year-to-date return based on net asset value for the period 12/31/2013 to 9/30/2014 was 16.06%.

rr_PerformanceTableHeading

AVERAGE ANNUAL TOTAL RETURNS FOR THE PERIODS ENDED DECEMBER 31, 2013

rr_RiskReturnAbstract

Fees Previously Waived or Expenses Reimbursed by First Trust

rr_ManagementFeesOverAssets

0.50%

rr_Component1OtherExpensesOverAssets

none

^[2],[3]

Total Net Annual Fund Operating Expenses After Fee Waiver and Expense Reimbursement

rr_ExpensesOverAssets

0.66%

rr_NetExpensesOverAssets

0.66%

rr_ExpenseExampleNoRedemptionYear03

263

rr_ExpenseExampleNoRedemptionYear10

1,095

rr_AnnualReturn2009

51.23%

rr_AnnualReturn2011

5.76%

rr_AnnualReturn2013

47.46%

rr_AverageAnnualReturnYear05

27.67%

rr_AverageAnnualReturnInceptionDate

May 08, 2007

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear05

27.61%

rr_AverageAnnualReturnYear01

26.86%

rr_AverageAnnualReturnSinceInception

11.64%

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear01

48.60%

rr_AverageAnnualReturnSinceInception

15.11%

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear01

33.11%

rr_AverageAnnualReturnSinceInception

5.66%

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear01

41.46%

rr_AverageAnnualReturnSinceInception

8.69%

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear01

42.30%

rr_AverageAnnualReturnSinceInception

rr_RiskReturnAbstract

rr_ObjectiveHeading

INVESTMENT OBJECTIVE

rr_ExpenseHeading

FEES AND EXPENSES OF THE FUND

rr_ShareholderFeesCaption

SHAREHOLDER FEES (fees paid directly from your investment)

rr_PortfolioTurnoverHeading

PORTFOLIO TURNOVER

rr_ExpenseExampleHeading

EXAMPLE

rr_StrategyHeading

PRINCIPAL INVESTMENT STRATEGIES

rr_RiskHeading

PRINCIPAL RISKS

rr_BarChartAndPerformanceTableHeading

ANNUAL TOTAL RETURN

rr_BarChartHeading

FIRST TRUST INDUSTRIALS/PRODUCER DURABLES ALPHADEX(R) FUND--TOTAL RETURNS(1)

Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)

rr_BarChartClosingTextBlock

During the six-year period ended December 31, 2013, the Fund's highest and lowest calendar quarter returns were 24.70% and -28.74%, respectively, for the quarters ended September 30, 2009 and December 31, 2008. The Fund's past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future.

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

rr_DistributionAndService12b1FeesOverAssets

none

^[1]

rr_OtherExpensesOverAssets

0.17%

rr_FeeWaiverOrReimbursementOverAssets

none

^[2]

rr_ExpenseExampleNoRedemptionYear01

68

rr_ExpenseExampleNoRedemptionYear05

483

rr_AnnualReturn2008

(45.90%)

rr_AnnualReturn2010

25.62%

rr_AnnualReturn2012

15.44%

rr_AverageAnnualReturnYear01

46.46%

rr_AverageAnnualReturnSinceInception

6.23%

rr_AverageAnnualReturnYear01

46.18%

rr_AverageAnnualReturnSinceInception

5.93%

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear05

18.90%

rr_AverageAnnualReturnLabel

(reflects no deduction for fees, expenses or taxes)

rr_AverageAnnualReturnYear05

24.17%

rr_AverageAnnualReturnLabel

(reflects no deduction for fees, expenses or taxes)

rr_AverageAnnualReturnYear05

18.59%

rr_AverageAnnualReturnLabel

(reflects no deduction for fees, expenses or taxes)

rr_AverageAnnualReturnYear05

19.84%

rr_AverageAnnualReturnLabel

(reflects no deduction for fees, expenses or taxes)

rr_AverageAnnualReturnYear05

20.16%

rr_RiskReturnHeading

SUMMARY INFORMATION

rr_ObjectivePrimaryTextBlock

The First Trust Materials AlphaDEX(R) Fund (the "Fund") seeks investment results that correspond generally to the price and yield (before the Fund's fees and expenses) of an equity index called the StrataQuant(R) Materials Index (the "Index").

rr_ExpenseNarrativeTextBlock

The following table describes the fees and expenses you may pay if you buy and hold shares of the Fund. Investors purchasing and selling shares may be subject to costs (including customary brokerage commissions) charged by their broker, which are not reflected in the table below.

rr_OperatingExpensesCaption

ANNUAL FUND OPERATING EXPENSES (expenses that you pay each year as a percentage of the value of your investment)

Expense Example, No Redemption Narrative [Text Block]

rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 76% of the average value of its portfolio.

rr_ExpenseExampleNoRedemptionNarrativeTextBlock

The example below is intended to help you compare the cost of investing in the Fund with the cost of investing in other funds. This example does not take into account customary brokerage commissions that you pay when purchasing or selling shares of the Fund in the secondary market.

The example assumes that you invest $10,000 in the Fund for the time periods indicated. The example also assumes that your investment has a 5% return each year and that the Fund's operating expenses remain at current levels. Additionally, the example assumes that the Fund imposes a 12b-1 fee of 0.25% per annum of the Fund's average daily net assets following December 31, 2015. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

rr_StrategyNarrativeTextBlock

The Fund will normally invest at least 90% (plus the amount of any borrowings for investment purposes) of its net assets in common stocks that comprise the Index. The Fund, using an "indexing" investment approach, attempts to replicate, before fees and expenses, the performance of the Index. First Trust seeks a correlation of 0.95 or better (before fees and expenses) between the Fund's performance and the performance of the Index; a figure of 1.00 would represent perfect correlation.

The Index is in the "StrataQuant(R) Series," a family of custom enhanced indices developed, maintained and sponsored by NYSE Group, Inc. or its affiliates ("NYSE" or an "Index Provider"), and licensed to First Trust Portfolios L.P. by NYSE. Prior to the acquisition of the American Stock Exchange LLC (the "AMEX") by NYSE, the equity indices in the StrataQuant(R) Series were developed, maintained and sponsored by the AMEX. The Index is a modified equal-dollar weighted index designed by NYSE to objectively identify and select stocks from the Russell 1000(R) Index in the materials and processing sector that may generate positive alpha relative to traditional passive-style indices through the use of the AlphaDEX(R) selection methodology. Alpha is an indication of how much an investment outperforms or underperforms on a risk-adjusted basis relative to its benchmark. As of July 31, 2014, the Index was comprised of 57 stocks. The Index is rebalanced and reconstituted as of the last business day of each calendar quarter. Changes to the Index will be effective at the open of trading on the fourth business day of the following month.

rr_RiskNarrativeTextBlock

You could lose money by investing in the Fund. An investment in the Fund is not a deposit of a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency. There can be no assurance that the Fund's investment objective will be achieved.

EQUITY SECURITIES RISK. Because the Fund invests in equity securities, the value of the Fund's shares will fluctuate with changes in the value of these equity securities. Equity securities prices fluctuate for several reasons, including changes in investors' perceptions of the financial condition of an issuer or the general condition of the relevant stock market, such as the current market volatility, or when political or economic events affecting the issuers occur. In addition, common stock prices may be particularly sensitive to rising interest rates, as the cost of capital rises and borrowing costs increase.

INDEX CORRELATION RISK. You should anticipate that the value of Fund shares will decline more or less in correlation with any decline in the value of the Fund's Index.

MARKET RISK. Market risk is the risk that the underlying securities in which the Fund invests, or shares of the Fund in general, may fall in value. Securities are subject to market fluctuations caused by such factors as economic, political, regulatory or market developments, changes in interest rates and perceived trends in securities prices. Overall securities values could decline generally or could underperform other investments.

MATERIALS AND PROCESSING COMPANIES RISK. The Fund invests in the securities of materials and processing companies, which are involved in the extracting or processing of raw materials. General risks of these companies include the general state of the economy, consolidation, domestic and international politics and excess capacity. In addition, materials companies may also be significantly affected by volatility of commodity prices, import controls, worldwide competition, liability for environmental damage, depletion of resources and mandated expenditures for safety and pollution control devices.

NON-CORRELATION RISK. The Fund's return may not match the return of the Index for a number of reasons. For example, the Fund incurs operating expenses not applicable to the Index, and may incur costs in buying and selling securities, especially when rebalancing the Fund's portfolio holdings to reflect changes in the composition of the Index. In addition, the Fund's portfolio holdings may not exactly replicate the securities included in the Index or the ratios between the securities included in the Index.

REPLICATION MANAGEMENT RISK. The Fund is exposed to additional market risk due to its policy of investing principally in the securities included in the Index. As a result of this policy, securities held by the Fund will generally not be bought or sold in response to market fluctuations, and the securities may be issued by companies concentrated in a particular industry if the Index is so concentrated. Therefore, the Fund will generally not sell a security because its issuer is in financial trouble, unless that security is removed or is anticipated to be removed from the Index.

SMALLER COMPANIES RISK. The Fund may invest in small and/or mid-capitalization companies. Such companies may be more vulnerable to adverse general market or economic developments, and their securities may be less liquid and may experience greater price volatility than larger, more established companies as a result of several factors, including limited trading volumes, products or financial resources, management inexperience and less publicly available information. Accordingly, such companies are generally subject to greater market risk than larger, more established companies.

rr_PerformanceNarrativeTextBlock

The bar chart and table below illustrate the annual calendar year returns of the Fund based on net asset value for the past six years as well as the average annual Fund and Index returns for the one year, five year and since inception periods ended December 31, 2013. The bar chart and table provide an 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 total returns based on net asset value compare to those of the Index, a broad-based market index and two specialized securities market indices. With respect to the Russell 1000(R) Materials and Processing Index, on or about September 18, 2008, Russell Investment Group ("Russell") began calculating its Russell U.S. Indices using an enhanced Russell sector scheme, the Russell Global Sectors (the "RGS"). The RGS and the former U.S. sector scheme ran in tandem until June 30, 2009, when Russell officially transitioned to the RGS and ceased calculating its indices using the U.S. sector scheme. Consequently, performance data is not available for the Russell 1000(R) Materials and Processing Index for the entire "5 Years" or "Since Inception" periods set forth in the table because performance data does not exist using solely the U.S. sector scheme or alternatively, using solely the RGS. See "Total Return Information" for additional performance information regarding the Fund. The Fund's performance information is accessible on the Fund's website at www.ftportfolios.com.

Returns before taxes do not reflect the effects of any income or capital gains taxes. All after-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of any state or local tax. Returns after taxes on distributions reflect the taxed return on the payment of dividends and capital gains. Returns after taxes on distributions and sale of shares assume you sold your shares at period end, and, therefore, are also adjusted for any capital gains or losses incurred. Returns for the market indices do not include expenses, which are deducted from Fund returns, or taxes.

Your own actual after-tax returns will depend on your specific tax situation and may differ from what is shown here. After-tax returns are not relevant to investors who hold Fund shares in tax-deferred accounts such as individual retirement accounts (IRAs) or employee-sponsored retirement plans.

rr_BarChartFootnotesTextBlock

(1) The Fund's year-to-date return based on net asset value for the period 12/31/2013 to 9/30/2014 was -0.08%.

rr_PerformanceTableHeading

AVERAGE ANNUAL TOTAL RETURNS FOR THE PERIODS ENDED DECEMBER 31, 2013

rr_RiskReturnAbstract

Fees Previously Waived or Expenses Reimbursed by First Trust

rr_ManagementFeesOverAssets

0.50%

rr_Component1OtherExpensesOverAssets

0.04%

^[2]

Total Net Annual Fund Operating Expenses After Fee Waiver and Expense Reimbursement

rr_ExpensesOverAssets

0.70%

rr_NetExpensesOverAssets

0.70%

rr_ExpenseExampleNoRedemptionYear03

276

rr_ExpenseExampleNoRedemptionYear10

1,141

rr_AnnualReturn2009

59.95%

rr_AnnualReturn2011

(10.11%)

rr_AnnualReturn2013

26.73%

rr_AverageAnnualReturnYear05

23.91%

rr_AverageAnnualReturnInceptionDate

May 08, 2007

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear05

23.25%

rr_AverageAnnualReturnYear01

15.09%

rr_AverageAnnualReturnSinceInception

6.94%

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear01

27.70%

rr_AverageAnnualReturnSinceInception

9.88%

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear01

33.11%

rr_AverageAnnualReturnSinceInception

5.66%

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear01

25.60%

rr_AverageAnnualReturnSinceInception

4.90%

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear01

25.15%

rr_AverageAnnualReturnSinceInception

rr_RiskReturnAbstract

rr_ObjectiveHeading

INVESTMENT OBJECTIVE

rr_ExpenseHeading

FEES AND EXPENSES OF THE FUND

rr_ShareholderFeesCaption

SHAREHOLDER FEES (fees paid directly from your investment)

rr_PortfolioTurnoverHeading

PORTFOLIO TURNOVER

rr_ExpenseExampleHeading

EXAMPLE

rr_StrategyHeading

PRINCIPAL INVESTMENT STRATEGIES

rr_RiskHeading

PRINCIPAL RISKS

rr_BarChartAndPerformanceTableHeading

ANNUAL TOTAL RETURN

rr_BarChartHeading

FIRST TRUST TECHNOLOGY ALPHADEX(R) FUND--TOTAL RETURNS(1)

Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)

rr_BarChartClosingTextBlock

During the six-year period ended December 31, 2013, the Fund's highest and lowest calendar quarter returns were 22.85% and -28.69%, respectively, for the quarters ended June 30, 2009 and December 31, 2008. The Fund's past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future.

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

rr_DistributionAndService12b1FeesOverAssets

none

^[1]

rr_OtherExpensesOverAssets

0.17%

rr_FeeWaiverOrReimbursementOverAssets

none

^[2]

rr_ExpenseExampleNoRedemptionYear01

68

rr_ExpenseExampleNoRedemptionYear05

483

rr_AnnualReturn2008

(48.07%)

rr_AnnualReturn2010

26.41%

rr_AnnualReturn2012

8.97%

rr_AverageAnnualReturnYear01

37.73%

rr_AverageAnnualReturnSinceInception

6.32%

rr_AverageAnnualReturnYear01

37.51%

rr_AverageAnnualReturnSinceInception

6.27%

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear05

18.80%

rr_AverageAnnualReturnLabel

(reflects no deduction for fees, expenses or taxes)

rr_AverageAnnualReturnYear05

23.87%

rr_AverageAnnualReturnLabel

(reflects no deduction for fees, expenses or taxes)

rr_AverageAnnualReturnYear05

18.59%

rr_AverageAnnualReturnLabel

(reflects no deduction for fees, expenses or taxes)

rr_AverageAnnualReturnYear05

21.90%

rr_AverageAnnualReturnLabel

(reflects no deduction for fees, expenses or taxes)

rr_AverageAnnualReturnYear05

21.51%

rr_RiskReturnHeading

SUMMARY INFORMATION

rr_ObjectivePrimaryTextBlock

The First Trust Utilities AlphaDEX(R) Fund (the "Fund") seeks investment results that correspond generally to the price and yield (before the Fund's fees and expenses) of an equity index called the StrataQuant(R) Utilities Index (the "Index").

rr_ExpenseNarrativeTextBlock

The following table describes the fees and expenses you may pay if you buy and hold shares of the Fund. Investors purchasing and selling shares may be subject to costs (including customary brokerage commissions) charged by their broker, which are not reflected in the table below.

rr_OperatingExpensesCaption

ANNUAL FUND OPERATING EXPENSES (expenses that you pay each year as a percentage of the value of your investment)

Expense Example, No Redemption Narrative [Text Block]

rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 83% of the average value of its portfolio.

rr_ExpenseExampleNoRedemptionNarrativeTextBlock

The example below is intended to help you compare the cost of investing in the Fund with the cost of investing in other funds. This example does not take into account customary brokerage commissions that you pay when purchasing or selling shares of the Fund in the secondary market.

The example assumes that you invest $10,000 in the Fund for the time periods indicated. The example also assumes that your investment has a 5% return each year and that the Fund's operating expenses remain at current levels. Additionally, the example assumes that the Fund imposes a 12b-1 fee of 0.25% per annum of the Fund's average daily net assets following December 31, 2015. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

rr_StrategyNarrativeTextBlock

The Fund will normally invest at least 90% (plus the amount of any borrowings for investment purposes) of its net assets in common stocks that comprise the Index. The Fund, using an "indexing" investment approach, attempts to replicate, before fees and expenses, the performance of the Index. First Trust seeks a correlation of 0.95 or better (before fees and expenses) between the Fund's performance and the performance of the Index; a figure of 1.00 would represent perfect correlation.

The Index is in the "StrataQuant(R) Series," a family of custom enhanced indices developed, maintained and sponsored by NYSE Group, Inc. or its affiliates ("NYSE" or an "Index Provider"), and licensed to First Trust Portfolios L.P. by NYSE. Prior to the acquisition of the American Stock Exchange LLC (the "AMEX") by NYSE, the equity indices in the StrataQuant(R) Series were developed, maintained and sponsored by the AMEX. The Index is a modified equal-dollar weighted index designed by NYSE to objectively identify and select stocks from the Russell 1000(R) Index in the utilities sector that may generate positive alpha relative to traditional passive-style indices through the use of the AlphaDEX(R) selection methodology. Alpha is an indication of how much an investment outperforms or underperforms on a risk-adjusted basis relative to its benchmark. As of July 31, 2014, the Index was comprised of 43 stocks. The Index is rebalanced and reconstituted as of the last business day of each calendar quarter. Changes to the Index will be effective at the open of trading on the fourth business day of the following month.

rr_RiskNarrativeTextBlock

You could lose money by investing in the Fund. An investment in the Fund is not a deposit of a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency. There can be no assurance that the Fund's investment objective will be achieved.

EQUITY SECURITIES RISK. Because the Fund invests in equity securities, the value of the Fund's shares will fluctuate with changes in the value of these equity securities. Equity securities prices fluctuate for several reasons, including changes in investors' perceptions of the financial condition of an issuer or the general condition of the relevant stock market, such as the current market volatility, or when political or economic events affecting the issuers occur. In addition, common stock prices may be particularly sensitive to rising interest rates, as the cost of capital rises and borrowing costs increase.

INDEX CORRELATION RISK. You should anticipate that the value of Fund shares will decline more or less in correlation with any decline in the value of the Fund's Index.

MARKET RISK. Market risk is the risk that the underlying securities in which the Fund invests, or shares of the Fund in general, may fall in value. Securities are subject to market fluctuations caused by such factors as economic, political, regulatory or market developments, changes in interest rates and perceived trends in securities prices. Overall securities values could decline generally or could underperform other investments.

NON-CORRELATION RISK. The Fund's return may not match the return of the Index for a number of reasons. For example, the Fund incurs operating expenses not applicable to the Index, and may incur costs in buying and selling securities, especially when rebalancing the Fund's portfolio holdings to reflect changes in the composition of the Index. In addition, the Fund's portfolio holdings may not exactly replicate the securities included in the Index or the ratios between the securities included in the Index.

REPLICATION MANAGEMENT RISK. The Fund is exposed to additional market risk due to its policy of investing principally in the securities included in the Index. As a result of this policy, securities held by the Fund will generally not be bought or sold in response to market fluctuations, and the securities may be issued by companies concentrated in a particular industry if the Index is so concentrated. Therefore, the Fund will generally not sell a security because its issuer is in financial trouble, unless that security is removed or is anticipated to be removed from the Index.

SMALLER COMPANIES RISK. The Fund may invest in small and/or mid-capitalization companies. Such companies may be more vulnerable to adverse general market or economic developments, and their securities may be less liquid and may experience greater price volatility than larger, more established companies as a result of several factors, including limited trading volumes, products or financial resources, management inexperience and less publicly available information. Accordingly, such companies are generally subject to greater market risk than larger, more established companies.

TELECOMMUNICATIONS COMPANIES RISK. The Fund invests in the securities of telecommunications companies. Telecommunications companies are subject to risks, which include increased competition and regulation by various regulatory authorities, the need to commit substantial capital and technological obsolescence.

UTILITIES COMPANIES RISK. The Fund invests in the securities of utilities companies. General problems of utilities companies include the imposition of rate caps, increased competition due to deregulation, the difficulty in obtaining an adequate return on invested capital or in financing large construction projects, the limitations on operations and increased costs and delays attributable to environmental considerations and the capital market's ability to absorb utility debt. In addition, taxes, government regulation, international politics, price and supply fluctuations, volatile interest rates and energy conservation may cause difficulties for utilities. All of such issuers have been experiencing certain of these problems in varying degrees.

rr_PerformanceNarrativeTextBlock

The bar chart and table below illustrate the annual calendar year returns of the Fund based on net asset value for the past six years as well as the average annual Fund and Index returns for the one year, five year and since inception periods ended December 31, 2013. The bar chart and table provide an 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 total returns based on net asset value compare to those of the Index, a broad-based market index and two specialized securities market indices. With respect to the Russell 1000(R) Utilities Index, on or about September 18, 2008, Russell Investment Group ("Russell") began calculating its Russell U.S. Indices using an enhanced Russell sector scheme, the Russell Global Sectors (the "RGS"). The RGS and the former U.S. sector scheme ran in tandem until June 30, 2009, when Russell officially transitioned to the RGS and ceased calculating its indices using the U.S. sector scheme. Consequently, performance data is not available for the Russell 1000(R) Utilities Index for the entire "5 Years" or "Since Inception" periods set forth in the table because performance data does not exist using solely the U.S. sector scheme or alternatively, using solely the RGS. See "Total Return Information" for additional performance information regarding the Fund. The Fund's performance information is accessible on the Fund's website at www.ftportfolios.com.

Returns before taxes do not reflect the effects of any income or capital gains taxes. All after-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of any state or local tax. Returns after taxes on distributions reflect the taxed return on the payment of dividends and capital gains. Returns after taxes on distributions and sale of shares assume you sold your shares at period end, and, therefore, are also adjusted for any capital gains or losses incurred. Returns for the market indices do not include expenses, which are deducted from Fund returns, or taxes.

Your own actual after-tax returns will depend on your specific tax situation and may differ from what is shown here. After-tax returns are not relevant to investors who hold Fund shares in tax-deferred accounts such as individual retirement accounts (IRAs) or employee-sponsored retirement plans.

rr_BarChartFootnotesTextBlock

(1) The Fund's year-to-date return based on net asset value for the period 12/31/2013 to 9/30/2014 was 13.24%.

rr_PerformanceTableHeading

AVERAGE ANNUAL TOTAL RETURNS FOR THE PERIODS ENDED DECEMBER 31, 2013

rr_RiskReturnAbstract

Fees Previously Waived or Expenses Reimbursed by First Trust

rr_ManagementFeesOverAssets

0.50%

rr_Component1OtherExpensesOverAssets

0.01%

^[2]

Total Net Annual Fund Operating Expenses After Fee Waiver and Expense Reimbursement

rr_ExpensesOverAssets

0.70%

rr_NetExpensesOverAssets

0.70%

rr_ExpenseExampleNoRedemptionYear03

276

rr_ExpenseExampleNoRedemptionYear10

1,141

rr_AnnualReturn2009

22.54%

rr_AnnualReturn2011

10.33%

rr_AnnualReturn2013

17.51%

rr_AverageAnnualReturnYear05

12.72%

rr_AverageAnnualReturnInceptionDate

May 08, 2007

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear05

11.46%

rr_AverageAnnualReturnYear01

9.87%

rr_AverageAnnualReturnSinceInception

2.16%

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear01

19.06%

rr_AverageAnnualReturnSinceInception

4.44%

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear01

33.11%

rr_AverageAnnualReturnSinceInception

5.66%

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear01

13.21%

rr_AverageAnnualReturnSinceInception

2.60%

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear01

14.94%

rr_AverageAnnualReturnSinceInception

rr_RiskReturnAbstract

rr_ObjectiveHeading

INVESTMENT OBJECTIVE

rr_ExpenseHeading

FEES AND EXPENSES OF THE FUND

rr_ShareholderFeesCaption

SHAREHOLDER FEES (fees paid directly from your investment)

rr_PortfolioTurnoverHeading

PORTFOLIO TURNOVER

rr_ExpenseExampleHeading

EXAMPLE

rr_StrategyHeading

PRINCIPAL INVESTMENT STRATEGIES

rr_RiskHeading

PRINCIPAL RISKS

rr_BarChartAndPerformanceTableHeading

ANNUAL TOTAL RETURN

rr_BarChartHeading

FIRST TRUST LARGE CAP CORE ALPHADEX(R) FUND--TOTAL RETURNS(1)

Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)

rr_BarChartClosingTextBlock

During the six-year period ended December 31, 2013, the Fund's highest and lowest calendar quarter returns were 21.20% and -23.68%, respectively, for the quarters ended June 30, 2009 and December 31, 2008. The Fund's past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future.

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

rr_DistributionAndService12b1FeesOverAssets

none

^[1]

rr_OtherExpensesOverAssets

0.14%

rr_FeeWaiverOrReimbursementOverAssets

none

^[2]

rr_ExpenseExampleNoRedemptionYear01

65

rr_ExpenseExampleNoRedemptionYear05

466

rr_AnnualReturn2008

(38.35%)

rr_AnnualReturn2010

20.66%

rr_AnnualReturn2012

14.39%

rr_AverageAnnualReturnYear01

35.77%

rr_AverageAnnualReturnSinceInception

6.08%

rr_AverageAnnualReturnYear01

35.10%

rr_AverageAnnualReturnSinceInception

5.64%

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear05

16.55%

rr_AverageAnnualReturnLabel

(reflects no deduction for fees, expenses or taxes)

rr_AverageAnnualReturnYear05

21.45%

rr_AverageAnnualReturnLabel

(reflects no deduction for fees, expenses or taxes)

rr_AverageAnnualReturnYear05

17.94%

rr_RiskReturnHeading

SUMMARY INFORMATION

rr_ObjectivePrimaryTextBlock

The First Trust Mid Cap Core AlphaDEX(R) Fund (the "Fund") seeks investment results that correspond generally to the price and yield (before the Fund's fees and expenses) of an equity index called the Defined Mid Cap Core Index (the "Index").

rr_ExpenseNarrativeTextBlock

The following table describes the fees and expenses you may pay if you buy and hold shares of the Fund. Investors purchasing and selling shares may be subject to costs (including customary brokerage commissions) charged by their broker, which are not reflected in the table below.

rr_OperatingExpensesCaption

ANNUAL FUND OPERATING EXPENSES (expenses that you pay each year as a percentage of the value of your investment)

Expense Example, No Redemption Narrative [Text Block]

rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 81% of the average value of its portfolio.

rr_ExpenseExampleNoRedemptionNarrativeTextBlock

The example below is intended to help you compare the cost of investing in the Fund with the cost of investing in other funds. This example does not take into account customary brokerage commissions that you pay when purchasing or selling shares of the Fund in the secondary market.

The example assumes that you invest $10,000 in the Fund for the time periods indicated. The example also assumes that your investment has a 5% return each year and that the Fund's operating expenses remain at current levels. Additionally, the example assumes that the Fund imposes a 12b-1 fee of 0.25% per annum of the Fund's average daily net assets following December 31, 2015. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

rr_StrategyNarrativeTextBlock

The Fund will normally invest at least 90% (plus the amount of any borrowings for investment purposes) of its net assets in common stocks that comprise the Index. The Fund, using an "indexing" investment approach, attempts to replicate, before fees and expenses, the performance of the Index. First Trust seeks a correlation of 0.95 or better (before fees and expenses) between the Fund's performance and the performance of the Index; a figure of 1.00 would represent perfect correlation.

The Index is in the "Defined Index Series," a family of custom enhanced indices developed, maintained and sponsored by S&P Dow Jones Indices LLC ("S&P" or an "Index Provider"). The Index is a modified equal-dollar weighted index designed by S&P to objectively identify and select stocks from the S&P MidCap 400(R) Index that may generate positive alpha relative to traditional passive-style indices through the use of the AlphaDEX(R) selection methodology. Alpha is an indication of how much an investment outperforms or underperforms on a risk-adjusted basis relative to its benchmark. The Fund may invest in common stocks and business development companies ("BDCs") that comprise the Index. As of July 31, 2014, the Index was comprised of 300 stocks and the market capitalization range represented in the Index was $1.19 billion to $11.41 billion. The Index is rebalanced and reconstituted as of the last business day of each calendar quarter. Changes to the Index will be effective at the open of trading on the sixth business day of the following month.

rr_RiskNarrativeTextBlock

You could lose money by investing in the Fund. An investment in the Fund is not a deposit of a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency. There can be no assurance that the Fund's investment objective will be achieved.

BDC RISK. The Fund may invest in BDCs which may carry risks similar to those of a private equity or venture capital fund. BDCs are not redeemable at the option of the shareholder and they may trade in the market at a discount to their net asset value. The BDCs held by the Fund may employ the use of leverage through borrowings or the issuance of preferred stock. While leverage often serves to increase the yield of a BDC, this leverage also subjects a BDC to increased risks, including the likelihood of increased volatility and the possibility that a BDC's common share income will fall if the dividend rate of the preferred shares or the interest rate on any borrowings rises.

EQUITY SECURITIES RISK. Because the Fund invests in equity securities, the value of the Fund's shares will fluctuate with changes in the value of these equity securities. Equity securities prices fluctuate for several reasons, including changes in investors' perceptions of the financial condition of an issuer or the general condition of the relevant stock market, such as the current market volatility, or when political or economic events affecting the issuers occur. In addition, common stock prices may be particularly sensitive to rising interest rates, as the cost of capital rises and borrowing costs increase.

INDEX CORRELATION RISK. You should anticipate that the value of Fund shares will decline more or less in correlation with any decline in the value of the Fund's Index.

INDUSTRIALS AND PRODUCER DURABLES COMPANIES RISK. The Fund invests in the securities of industrials and producer durables companies, which convert unfinished goods into finished durables used to manufacture other goods or provide services. These companies produce electrical equipment and components, industrial products, manufactured housing and telecommunications equipment. General risks of these companies include the general state of the economy, intense competition, consolidation, domestic and international politics, excess capacity and consumer demand and spending trends. In addition, they may also be significantly affected by overall capital spending levels, economic cycles, technical obsolescence, delays in modernization, labor relations, government regulations and e-commerce initiatives.

MARKET CAPITALIZATION RISK. The Fund normally invests at least 90% of its assets in common stocks that comprise the Index. The securities of companies represented in the Index generally have market capitalizations that are consistent with the name of the Index. To determine the market capitalization range of such securities, the Fund uses the current range of the Index. However, the Fund will not sell a security because the security has exceeded or fallen below the current market capitalization range of the Index. Because of market movement, there can be no assurance that the securities in the Fund will stay within a given market capitalization range. As a result, the Fund may be exposed to additional risk or may not give investors the opportunity to invest fully in a given market capitalization range.

MARKET RISK. Market risk is the risk that the underlying securities in which the Fund invests, or shares of the Fund in general, may fall in value. Securities are subject to market fluctuations caused by such factors as economic, political, regulatory or market developments, changes in interest rates and perceived trends in securities prices. Overall securities values could decline generally or could underperform other investments.

NON-CORRELATION RISK. The Fund's return may not match the return of the Index for a number of reasons. For example, the Fund incurs operating expenses not applicable to the Index, and may incur costs in buying and selling securities, especially when rebalancing the Fund's portfolio holdings to reflect changes in the composition of the Index. In addition, the Fund's portfolio holdings may not exactly replicate the securities included in the Index or the ratios between the securities included in the Index.

REPLICATION MANAGEMENT RISK. The Fund is exposed to additional market risk due to its policy of investing principally in the securities included in the Index. As a result of this policy, securities held by the Fund will generally not be bought or sold in response to market fluctuations, and the securities may be issued by companies concentrated in a particular industry if the Index is so concentrated. Therefore, the Fund will generally not sell a security because its issuer is in financial trouble, unless that security is removed or is anticipated to be removed from the Index.

SMALLER COMPANIES RISK. The Fund invests in mid-capitalization companies. Such companies may be more vulnerable to adverse general market or economic developments, and their securities may be less liquid and may experience greater price volatility than larger, more established companies as a result of several factors, including limited trading volumes, products or financial resources, management inexperience and less publicly available information. Accordingly, such companies are generally subject to greater market risk than larger, more established companies.

rr_PerformanceNarrativeTextBlock

The bar chart and table below illustrate the annual calendar year returns of the Fund based on net asset value for the past six years as well as the average annual Fund and Index returns for the one year, five year and since inception periods ended December 31, 2013. The bar chart and table provide an 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 total returns based on net asset value compare to those of the Index and a broad-based market index. See "Total Return Information" for additional performance information regarding the Fund. The Fund's performance information is accessible on the Fund's website at www.ftportfolios.com.

Returns before taxes do not reflect the effects of any income or capital gains taxes. All after-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of any state or local tax. Returns after taxes on distributions reflect the taxed return on the payment of dividends and capital gains. Returns after taxes on distributions and sale of shares assume you sold your shares at period end, and, therefore, are also adjusted for any capital gains or losses incurred. Returns for the market index do not include expenses, which are deducted from Fund returns, or taxes.

Your own actual after-tax returns will depend on your specific tax situation and may differ from what is shown here. After-tax returns are not relevant to investors who hold Fund shares in tax-deferred accounts such as individual retirement accounts (IRAs) or employee-sponsored retirement plans.

rr_BarChartFootnotesTextBlock

(1) The Fund's year-to-date return based on net asset value for the period 12/31/2013 to 9/30/2014 was 0.13%.

rr_PerformanceTableHeading

AVERAGE ANNUAL TOTAL RETURNS FOR THE PERIODS ENDED DECEMBER 31, 2013

rr_RiskReturnAbstract

Fees Previously Waived or Expenses Reimbursed by First Trust

rr_ManagementFeesOverAssets

0.50%

rr_Component1OtherExpensesOverAssets

none

^[2]

Acquired Fund Fees and Expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.03%

^[4]

rr_FeeWaiverOrReimbursementOverAssets

none

^[2]

rr_ExpenseExampleNoRedemptionYear01

68

rr_ExpenseExampleNoRedemptionYear05

483

rr_AnnualReturn2008

(36.77%)

rr_AnnualReturn2010

27.03%

rr_AnnualReturn2012

14.23%

rr_AverageAnnualReturnYear01

37.45%

rr_AverageAnnualReturnSinceInception

8.87%

rr_AverageAnnualReturnYear01

37.00%

rr_AverageAnnualReturnSinceInception

8.59%

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear05

19.89%

rr_AverageAnnualReturnLabel

(reflects no deduction for fees, expenses or taxes)

rr_AverageAnnualReturnYear05

25.23%

rr_AverageAnnualReturnLabel

(reflects no deduction for fees, expenses or taxes)

rr_AverageAnnualReturnYear05

21.89%

rr_RiskReturnHeading

SUMMARY INFORMATION

rr_ObjectivePrimaryTextBlock

The First Trust Small Cap Core AlphaDEX(R) Fund (the "Fund") seeks investment results that correspond generally to the price and yield (before the Fund's fees and expenses) of an equity index called the Defined Small Cap Core Index (the "Index").

rr_ExpenseNarrativeTextBlock

The following table describes the fees and expenses you may pay if you buy and hold shares of the Fund. Investors purchasing and selling shares may be subject to costs (including customary brokerage commissions) charged by their broker, which are not reflected in the table below.

rr_OperatingExpensesCaption

ANNUAL FUND OPERATING EXPENSES (expenses that you pay each year as a percentage of the value of your investment)

Expense Example, No Redemption Narrative [Text Block]

rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 89% of the average value of its portfolio.

rr_ExpenseExampleNoRedemptionNarrativeTextBlock

The example below is intended to help you compare the cost of investing in the Fund with the cost of investing in other funds. This example does not take into account customary brokerage commissions that you pay when purchasing or selling shares of the Fund in the secondary market.

The example assumes that you invest $10,000 in the Fund for the time periods indicated. The example also assumes that your investment has a 5% return each year and that the Fund's operating expenses remain at current levels. Additionally, the example assumes that the Fund imposes a 12b-1 fee of 0.25% per annum of the Fund's average daily net assets following December 31, 2015. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

rr_StrategyNarrativeTextBlock

The Fund will normally invest at least 90% (plus the amount of any borrowings for investment purposes) of its net assets in common stocks that comprise the Index. The Fund, using an "indexing" investment approach, attempts to replicate, before fees and expenses, the performance of the Index. First Trust seeks a correlation of 0.95 or better (before fees and expenses) between the Fund's performance and the performance of the Index; a figure of 1.00 would represent perfect correlation.

The Index is in the "Defined Index Series," a family of custom enhanced indices developed, maintained and sponsored by S&P Dow Jones Indices LLC ("S&P" or an "Index Provider"). The Index is a modified equal-dollar weighted index designed by S&P to objectively identify and select stocks from the S&P SmallCap 600(R) Index that may generate positive alpha relative to traditional passive-style indices through the use of the AlphaDEX(R) selection methodology. Alpha is an indication of how much an investment outperforms or underperforms on a risk-adjusted basis relative to its benchmark. The Fund may invest in common stocks and business development companies ("BDCs") that comprise the Index. As of July 31, 2014, the Index was comprised of 447 stocks and the market capitalization range represented in the Index was $199 million to $5.52 billion. The Index is rebalanced and reconstituted as of the last business day of each calendar quarter. Changes to the Index will be effective at the open of trading on the sixth business day of the following month.

rr_RiskNarrativeTextBlock

You could lose money by investing in the Fund. An investment in the Fund is not a deposit of a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency. There can be no assurance that the Fund's investment objective will be achieved.

BDC RISK. The Fund may invest in BDCs which may carry risks similar to those of a private equity or venture capital fund. BDCs are not redeemable at the option of the shareholder and they may trade in the market at a discount to their net asset value. The BDCs held by the Fund may employ the use of leverage through borrowings or the issuance of preferred stock. While leverage often serves to increase the yield of a BDC, this leverage also subjects a BDC to increased risks, including the likelihood of increased volatility and the possibility that a BDC's common share income will fall if the dividend rate of the preferred shares or the interest rate on any borrowings rises.

EQUITY SECURITIES RISK. Because the Fund invests in equity securities, the value of the Fund's shares will fluctuate with changes in the value of these equity securities. Equity securities prices fluctuate for several reasons, including changes in investors' perceptions of the financial condition of an issuer or the general condition of the relevant stock market, such as the current market volatility, or when political or economic events affecting the issuers occur. In addition, common stock prices may be particularly sensitive to rising interest rates, as the cost of capital rises and borrowing costs increase.

INDEX CORRELATION RISK. You should anticipate that the value of Fund shares will decline more or less in correlation with any decline in the value of the Fund's Index.

MARKET CAPITALIZATION RISK. The Fund normally invests at least 90% of its assets in common stocks that comprise the Index. The securities of companies represented in the Index generally have market capitalizations that are consistent with the name of the Index. To determine the market capitalization range of such securities, the Fund uses the current range of the Index. However, the Fund will not sell a security because the security has exceeded or fallen below the current market capitalization range of the Index. Because of market movement, there can be no assurance that the securities in the Fund will stay within a given market capitalization range. As a result, the Fund may be exposed to additional risk or may not give investors the opportunity to invest fully in a given market capitalization range. Because the Fund invests in small capitalization companies, the Fund is more vulnerable to adverse general market or economic developments, may be less liquid, and may experience greater price volatility than larger, more established companies.

MARKET RISK. Market risk is the risk that the underlying securities in which the Fund invests, or shares of the Fund in general, may fall in value. Securities are subject to market fluctuations caused by such factors as economic, political, regulatory or market developments, changes in interest rates and perceived trends in securities prices. Overall securities values could decline generally or could underperform other investments.

NON-CORRELATION RISK. The Fund's return may not match the return of the Index for a number of reasons. For example, the Fund incurs operating expenses not applicable to the Index, and may incur costs in buying and selling securities, especially when rebalancing the Fund's portfolio holdings to reflect changes in the composition of the Index. In addition, the Fund's portfolio holdings may not exactly replicate the securities included in the Index or the ratios between the securities included in the Index.

REPLICATION MANAGEMENT RISK. The Fund is exposed to additional market risk due to its policy of investing principally in the securities included in the Index. As a result of this policy, securities held by the Fund will generally not be bought or sold in response to market fluctuations, and the securities may be issued by companies concentrated in a particular industry if the Index is so concentrated. Therefore, the Fund will generally not sell a security because its issuer is in financial trouble, unless that security is removed or is anticipated to be removed from the Index.

SMALLER COMPANIES RISK. The Fund invests in small-capitalization companies. Such companies may be more vulnerable to adverse general market or economic developments, and their securities may be less liquid and may experience greater price volatility than larger, more established companies as a result of several factors, including limited trading volumes, products or financial resources, management inexperience and less publicly available information. Accordingly, such companies are generally subject to greater market risk than larger, more established companies.

rr_PerformanceNarrativeTextBlock

The bar chart and table below illustrate the annual calendar year returns of the Fund based on net asset value for the past six years as well as the average annual Fund and Index returns for the one year, five year and since inception periods ended December 31, 2013. The bar chart and table provide an 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 total returns based on net asset value compare to those of the Index and a broad-based market index. See "Total Return Information" for additional performance information regarding the Fund. The Fund's performance information is accessible on the Fund's website at www.ftportfolios.com.

Returns before taxes do not reflect the effects of any income or capital gains taxes. All after-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of any state or local tax. Returns after taxes on distributions reflect the taxed return on the payment of dividends and capital gains. Returns after taxes on distributions and sale of shares assume you sold your shares at period end, and, therefore, are also adjusted for any capital gains or losses incurred. Returns for the market index do not include expenses, which are deducted from Fund returns, or taxes.

Your own actual after-tax returns will depend on your specific tax situation and may differ from what is shown here. After-tax returns are not relevant to investors who hold Fund shares in tax-deferred accounts such as individual retirement accounts (IRAs) or employee-sponsored retirement plans.

rr_BarChartFootnotesTextBlock

(1) The Fund's year-to-date return based on net asset value for the period 12/31/2013 to 9/30/2014 was -7.60%.

rr_PerformanceTableHeading

AVERAGE ANNUAL TOTAL RETURNS FOR THE PERIODS ENDED DECEMBER 31, 2013

rr_RiskReturnAbstract

Fees Previously Waived or Expenses Reimbursed by First Trust

rr_ManagementFeesOverAssets

0.50%

rr_Component1OtherExpensesOverAssets

none

^[2],[3]

Acquired Fund Fees and Expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.02%

^[4]

rr_FeeWaiverOrReimbursementOverAssets

none

^[2]

rr_ExpenseExampleNoRedemptionYear01

68

rr_ExpenseExampleNoRedemptionYear05

483

rr_AnnualReturn2008

(34.28%)

rr_AnnualReturn2010

26.92%

rr_AnnualReturn2012

15.39%

rr_AverageAnnualReturnYear01

43.15%

rr_AverageAnnualReturnSinceInception

8.04%

rr_AverageAnnualReturnYear01

42.90%

rr_AverageAnnualReturnSinceInception

7.86%

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear05

19.26%

rr_AverageAnnualReturnLabel

(reflects no deduction for fees, expenses or taxes)

rr_AverageAnnualReturnYear05

24.47%

rr_AverageAnnualReturnLabel

(reflects no deduction for fees, expenses or taxes)

rr_AverageAnnualReturnYear05

21.37%

rr_RiskReturnHeading

SUMMARY INFORMATION

rr_ObjectivePrimaryTextBlock

The First Trust Large Cap Value AlphaDEX(R) Fund (the "Fund") seeks investment results that correspond generally to the price and yield (before the Fund's fees and expenses) of an equity index called the Defined Large Cap Value Index (the "Index").

rr_ExpenseNarrativeTextBlock

The following table describes the fees and expenses you may pay if you buy and hold shares of the Fund. Investors purchasing and selling shares may be subject to costs (including customary brokerage commissions) charged by their broker, which are not reflected in the table below.

rr_OperatingExpensesCaption

ANNUAL FUND OPERATING EXPENSES (expenses that you pay each year as a percentage of the value of your investment)

Expense Example, No Redemption Narrative [Text Block]

rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 68% of the average value of its portfolio.

rr_ExpenseExampleNoRedemptionNarrativeTextBlock

The example below is intended to help you compare the cost of investing in the Fund with the cost of investing in other funds. This example does not take into account customary brokerage commissions that you pay when purchasing or selling shares of the Fund in the secondary market.

The example assumes that you invest $10,000 in the Fund for the time periods indicated. The example also assumes that your investment has a 5% return each year and that the Fund's operating expenses remain at current levels. Additionally, the example assumes that the Fund imposes a 12b-1 fee of 0.25% per annum of the Fund's average daily net assets following December 31, 2015. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

rr_StrategyNarrativeTextBlock

The Fund will normally invest at least 90% (plus the amount of any borrowings for investment purposes) of its net assets in common stocks that comprise the Index. The Fund, using an "indexing" investment approach, attempts to replicate, before fees and expenses, the performance of the Index. First Trust seeks a correlation of 0.95 or better (before fees and expenses) between the Fund's performance and the performance of the Index; a figure of 1.00 would represent perfect correlation.

The Index is in the "Defined Index Series," a family of custom enhanced indices developed, maintained and sponsored by S&P Dow Jones Indices LLC ("S&P" or an "Index Provider"). The Index is a modified equal-dollar weighted index designed by S&P to objectively identify and select stocks from the S&P 500(R) Value Index that may generate positive alpha relative to traditional passive-style indices through the use of the AlphaDEX(R) selection methodology. Alpha is an indication of how much an investment outperforms or underperforms on a risk-adjusted basis relative to its benchmark. As of July 31, 2014, the Index was comprised of 190 stocks and the market capitalization range represented in the Index was $3.80 billion to $421.95 billion. The Index is rebalanced and reconstituted as of the last business day of each calendar quarter. Changes to the Index will be effective at the open of trading on the sixth business day of the following month.

rr_RiskNarrativeTextBlock

You could lose money by investing in the Fund. An investment in the Fund is not a deposit of a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency. There can be no assurance that the Fund's investment objective will be achieved.

ENERGY COMPANIES RISK. The Fund invests in the securities of energy companies, which include integrated oil companies that are involved in the exploration, production and refining process, gas distributors and pipeline-related companies and other energy companies involved with mining, producing and delivering energy-related services and drilling. General problems of energy companies include volatile fluctuations in price and supply of energy fuels, international politics, terrorist attacks, reduced demand, the success of exploration projects, clean-up and litigation costs relating to oil spills and environmental damage, and tax and other regulatory policies of various governments. Natural disasters such as hurricanes in the Gulf of Mexico also impact the petroleum industry. Oil production and refining companies are subject to extensive federal, state and local environmental laws and regulations regarding air emissions and the disposal of hazardous materials. In addition, oil prices are generally subject to extreme volatility.

EQUITY SECURITIES RISK. Because the Fund invests in equity securities, the value of the Fund's shares will fluctuate with changes in the value of these equity securities. Equity securities prices fluctuate for several reasons, including changes in investors' perceptions of the financial condition of an issuer or the general condition of the relevant stock market, such as the current market volatility, or when political or economic events affecting the issuers occur. In addition, common stock prices may be particularly sensitive to rising interest rates, as the cost of capital rises and borrowing costs increase.

INDEX CORRELATION RISK. You should anticipate that the value of Fund shares will decline more or less in correlation with any decline in the value of the Fund's Index.

MARKET CAPITALIZATION RISK. The Fund normally invests at least 90% of its assets in common stocks that comprise the Index. The securities of companies represented in the Index generally have market capitalizations that are consistent with the name of the Index. To determine the market capitalization range of such securities, the Fund uses the current range of the Index. However, the Fund will not sell a security because the security has exceeded or fallen below the current market capitalization range of the Index. Because of market movement, there can be no assurance that the securities in the Fund will stay within a given market capitalization range. As a result, the Fund may be exposed to additional risk or may not give investors the opportunity to invest fully in a given market capitalization range.

MARKET RISK. Market risk is the risk that the underlying securities in which the Fund invests, or shares of the Fund in general, may fall in value. Securities are subject to market fluctuations caused by such factors as economic, political, regulatory or market developments, changes in interest rates and perceived trends in securities prices. Overall securities values could decline generally or could underperform other investments.

NON-CORRELATION RISK. The Fund's return may not match the return of the Index for a number of reasons. For example, the Fund incurs operating expenses not applicable to the Index, and may incur costs in buying and selling securities, especially when rebalancing the Fund's portfolio holdings to reflect changes in the composition of the Index. In addition, the Fund's portfolio holdings may not exactly replicate the securities included in the Index or the ratios between the securities included in the Index.

REPLICATION MANAGEMENT RISK. The Fund is exposed to additional market risk due to its policy of investing principally in the securities included in the Index. As a result of this policy, securities held by the Fund will generally not be bought or sold in response to market fluctuations, and the securities may be issued by companies concentrated in a particular industry if the Index is so concentrated. Therefore, the Fund will generally not sell a security because its issuer is in financial trouble, unless that security is removed or is anticipated to be removed from the Index.

VALUE INVESTMENT STYLE RISK. Value companies may experience adverse business developments or may be subject to special risks that cause their securities to be out of favor, may never reach what may be their full value or may go down in price.

rr_PerformanceNarrativeTextBlock

The bar chart and table below illustrate the annual calendar year returns of the Fund based on net asset value for the past six years as well as the average annual Fund and Index returns for the one year, five year and since inception periods ended December 31, 2013. The bar chart and table provide an 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 total returns based on net asset value compare to those of the Index, a broad-based market index and a specialized securities market index. See "Total Return Information" for additional performance information regarding the Fund. The Fund's performance information is accessible on the Fund's website at www.ftportfolios.com.

Returns before taxes do not reflect the effects of any income or capital gains taxes. All after-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of any state or local tax. Returns after taxes on distributions reflect the taxed return on the payment of dividends and capital gains. Returns after taxes on distributions and sale of shares assume you sold your shares at period end, and, therefore, are also adjusted for any capital gains or losses incurred. Returns for the market indices do not include expenses, which are deducted from Fund returns, or taxes.

Your own actual after-tax returns will depend on your specific tax situation and may differ from what is shown here. After-tax returns are not relevant to investors who hold Fund shares in tax-deferred accounts such as individual retirement accounts (IRAs) or employee-sponsored retirement plans.

rr_BarChartFootnotesTextBlock

(1) The Fund's year-to-date return based on net asset value for the period 12/31/2013 to 9/30/2014 was 7.03%.

rr_PerformanceTableHeading

AVERAGE ANNUAL TOTAL RETURNS FOR THE PERIODS ENDED DECEMBER 31, 2013

rr_RiskReturnAbstract

Fees Previously Waived or Expenses Reimbursed by First Trust

rr_ManagementFeesOverAssets

0.50%

rr_Component1OtherExpensesOverAssets

none

^[2]

Total Net Annual Fund Operating Expenses After Fee Waiver and Expense Reimbursement

rr_ExpensesOverAssets

0.64%

rr_NetExpensesOverAssets

0.64%

rr_ExpenseExampleNoRedemptionYear03

257

rr_ExpenseExampleNoRedemptionYear10

1,071

rr_AnnualReturn2009

41.18%

rr_AnnualReturn2011

1.32%

rr_AnnualReturn2013

33.92%

rr_AverageAnnualReturnYear05

21.64%

rr_AverageAnnualReturnInceptionDate

May 08, 2007

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear05

20.94%

rr_AverageAnnualReturnYear01

19.15%

rr_AverageAnnualReturnSinceInception

4.59%

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear01

34.93%

rr_AverageAnnualReturnSinceInception

7.11%

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear01

32.39%

rr_AverageAnnualReturnSinceInception

5.39%

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear01

31.99%

rr_AverageAnnualReturnSinceInception

3.31%

rr_RiskReturnAbstract

rr_ObjectiveHeading

INVESTMENT OBJECTIVE

rr_ExpenseHeading

FEES AND EXPENSES OF THE FUND

rr_ShareholderFeesCaption

SHAREHOLDER FEES (fees paid directly from your investment)

rr_PortfolioTurnoverHeading

PORTFOLIO TURNOVER

rr_ExpenseExampleHeading

EXAMPLE

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PRINCIPAL INVESTMENT STRATEGIES

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PRINCIPAL RISKS

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ANNUAL TOTAL RETURN

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FIRST TRUST LARGE CAP GROWTH ALPHADEX(R) FUND--TOTAL RETURNS(1)

Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)

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During the six-year period ended December 31, 2013, the Fund's highest and lowest calendar quarter returns were 18.05% and -22.58%, respectively, for the quarters ended September 30, 2009 and December 31, 2008. The Fund's past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future.

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none

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none

^[1]

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0.15%

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none

^[2]

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66

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472

rr_AnnualReturn2008

(41.12%)

rr_AnnualReturn2010

23.67%

rr_AnnualReturn2012

9.92%

rr_AverageAnnualReturnYear01

37.71%

rr_AverageAnnualReturnSinceInception

5.45%

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37.40%

rr_AverageAnnualReturnSinceInception

5.21%

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15.09%

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(reflects no deduction for fees, expenses or taxes)

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19.61%

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(reflects no deduction for fees, expenses or taxes)

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17.94%

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(reflects no deduction for fees, expenses or taxes)

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19.24%

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SUMMARY INFORMATION

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The First Trust Multi Cap Value AlphaDEX(R) Fund (the "Fund") seeks investment results that correspond generally to the price and yield (before the Fund's fees and expenses) of an equity index called the Defined Multi Cap Value Index (the "Index").

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The following table describes the fees and expenses you may pay if you buy and hold shares of the Fund. Investors purchasing and selling shares may be subject to costs (including customary brokerage commissions) charged by their broker, which are not reflected in the table below.

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ANNUAL FUND OPERATING EXPENSES (expenses that you pay each year as a percentage of the value of your investment)

Expense Example, No Redemption Narrative [Text Block]

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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 shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 74% of the average value of its portfolio.

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The example below is intended to help you compare the cost of investing in the Fund with the cost of investing in other funds. This example does not take into account customary brokerage commissions that you pay when purchasing or selling shares of the Fund in the secondary market.

The example assumes that you invest $10,000 in the Fund for the time periods indicated. The example also assumes that your investment has a 5% return each year and that the Fund's operating expenses remain at current levels until November 30, 2015. Additionally, the example assumes that the Fund imposes a 12b-1 fee of 0.25% per annum of the Fund's average daily net assets following December 31, 2015. The example assumes that First Trust's agreement to waive fees and/or pay the Fund's expenses to the extent necessary to prevent the operating expenses of the Fund (excluding interest expense, brokerage commissions and other trading expenses, taxes, and extraordinary expenses) from exceeding 0.70% of average daily net assets per year will be terminated following November 30, 2015. Although your actual costs may be higher or lower, based on these assumptions your costs would be: