rr_RiskReturnHeading

SUMMARY INFORMATION

rr_ObjectivePrimaryTextBlock

The First Trust Consumer Discretionary 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 Discretionary Index (the "Index").

Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of Offering Price)

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.

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

rr_ManagementFeesOverAssets

0.50%

rr_OtherExpensesOverAssets

0.22%

rr_FeeWaiverOrReimbursementOverAssets

(0.02%)

^[1]

rr_PortfolioTurnoverHeading

Portfolio Turnover

rr_PortfolioTurnoverRate

98.00%

rr_ExpenseExampleNarrativeTextBlock

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 and then you retain the Shares or redeem all of your Shares at the end of those periods. The example also assumes that your investment has a 5% return each year and that the Fund's net annual operating expenses remain at current levels until November 30, 2013. 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 November 30, 2013. 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, 2013. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

rr_ExpenseExampleNoRedemptionYear03

273

rr_ExpenseExampleNoRedemptionYear10

1,156

rr_StrategyNarrativeTextBlock

The Fund will normally invest at least 90% 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. First Trust will regularly monitor the Fund's tracking accuracy and will seek to maintain an appropriate correlation.

The Index is in the "StrataQuant(R) Series," a family of custom enhanced indices developed, maintained and sponsored by NYSE Euronext or its affiliates ("NYSE Euronext" or an "Index Provider"), and licensed to First Trust Portfolios L.P. by NYSE Group, Inc. ("NYSE Group"), an affiliate of NYSE Euronext. Prior to the acquisition of the American Stock Exchange LLC (the "AMEX") by NYSE Euronext, 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 Euronext to objectively identify and select stocks from the Russell 1000(R) Index in the consumer discretionary 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, 2012, the Index was comprised of 123 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.

The Fund may lend securities representing up to 20% of the value of its total assets to broker-dealers, banks and other institutions to generate additional income. When the Fund loans its portfolio securities, it will receive, at the inception of each loan, cash collateral equal to at least 102% (for domestic securities) or 105% (for international securities) of the market value of the loaned securities.

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.

MARKET RISK. Market risk is the risk that a particular stock owned by the Fund, Shares of the Fund or stocks in general may fall in value. Shares are subject to market fluctuations caused by such factors as economic, political, regulatory or market developments, changes in interest rates and perceived trends in stock prices. Overall stock values could decline generally or could underperform other investments. Companies with smaller market capitalizations are generally subject to additional market risk.

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. Therefore, the Fund will generally not sell a stock because the stock's issuer is in financial trouble, unless that stock is removed or is anticipated to be removed from the Index.

NON-DIVERSIFICATION RISK. The Fund is classified as "non-diversified" under the Investment Company Act of 1940, as amended (the "1940 Act"). As a result, the Fund is only limited as to the percentage of its assets which may be invested in the securities of any one issuer by the diversification requirements imposed by the Internal Revenue Code of 1986, as amended (the "Code"). The Fund may invest a relatively high percentage of its assets in a limited number of issuers.

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

CONSUMER DISCRETIONARY SECTOR RISK. The Fund invests in the securities of companies in the consumer discretionary sector to approximately the same extent as the Index. Companies in the consumer discretionary sector manufacture products and provide discretionary services directly to the consumer, and the success of these companies is tied closely to the performance of the overall domestic and international economy, interest rates, competition and consumer confidence. Success depends heavily on disposable household income and consumer spending. Changes in demographics and consumer tastes can also affect the demand for, and success of, consumer discretionary products in the marketplace.

SECURITIES LENDING RISK. The Fund may engage in securities lending. Securities lending involves the risk that the Fund may lose money because the borrower of the Fund's loaned securities fails to return the securities in a timely manner or at all. The Fund could also lose money in the event of a decline in the value of the collateral provided for the loaned securities or a decline in the value of any investments made with cash collateral. These events could also trigger adverse tax consequences for the Fund.

rr_PerformanceNarrativeTextBlock

The bar chart and table below illustrate the annual calendar year returns of the Fund based on NAV for the past four years as well as the average annual Fund and Index returns for the one year and since inception periods ended December 31, 2011. 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 NAV 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 Discretionary Index (formerly the Russell 1000(R) Consumer Discretionary and 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) Consumer Discretionary Index for the entire "Since Inception" period 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_AnnualReturn2008

(42.87%)

rr_AnnualReturn2010

31.98%

rr_BarChartFootnotesTextBlock

The Fund's year-to-date return based on NAV for the period 12/31/2011 to 9/30/2012 was 11.74%.

rr_PerformanceTableHeading

Average Annual Total Returns for the Periods Ended December 31, 2011

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear01

0.98%

rr_AverageAnnualReturnInceptionDate

May 08, 2007

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear01

0.76%

rr_AverageAnnualReturnInceptionDate

May 08, 2007

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear01

0.64%

rr_AverageAnnualReturnInceptionDate

May 08, 2007

rr_RiskReturnAbstract

rr_AverageAnnualReturnSinceInception

1.23%

rr_AverageAnnualReturnYear01

1.50%

rr_AverageAnnualReturnInceptionDate

May 08, 2007

rr_RiskReturnAbstract

rr_AverageAnnualReturnSinceInception

1.54%

rr_AverageAnnualReturnYear01

5.39%

rr_AverageAnnualReturnInceptionDate

May 08, 2007

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_OperatingExpensesCaption

Annual Fund Operating Expenses (Expenses that you pay each year as a percentage of the value of your investment)

rr_DistributionAndService12b1FeesOverAssets

none

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

rr_ExpensesOverAssets

0.74%

rr_NetExpensesOverAssets

0.70%

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 126% of the average value of its portfolio.

rr_ExpenseExampleHeading

Example

rr_ExpenseExampleNoRedemptionYear01

72

rr_ExpenseExampleNoRedemptionYear05

509

rr_StrategyHeading

Principal Investment Strategies

rr_RiskHeading

Principal Risks

rr_BarChartAndPerformanceTableHeading

Annual Total Return

rr_BarChartHeading

Calendar Year Total Returns as of 12/31

rr_AnnualReturn2009

27.13%

rr_AnnualReturn2011

13.15%

rr_BarChartClosingTextBlock

During the four-year period ended December 31, 2011, the Fund's highest and lowest calendar quarter returns were 16.50% and -17.59%, 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_AverageAnnualReturnLabel

Return Before Taxes

rr_AverageAnnualReturnSinceInception

4.84%

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions

rr_AverageAnnualReturnSinceInception

4.42%

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions and Sale of Shares

rr_AverageAnnualReturnSinceInception

3.89%

rr_AverageAnnualReturnYear01

1.50%

rr_AverageAnnualReturnInceptionDate

May 08, 2007

rr_RiskReturnAbstract

rr_AverageAnnualReturnSinceInception

5.62%

rr_AverageAnnualReturnYear01

13.99%

rr_AverageAnnualReturnInceptionDate

May 08, 2007

rr_RiskReturnAbstract

rr_AverageAnnualReturnSinceInception

none

rr_RiskReturnHeading

SUMMARY INFORMATION

rr_ObjectivePrimaryTextBlock

The First Trust Energy 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) Energy Index (the "Index").

Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of Offering Price)

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.

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

rr_ManagementFeesOverAssets

0.50%

rr_OtherExpensesOverAssets

0.26%

rr_FeeWaiverOrReimbursementOverAssets

(0.06%)

^[1]

rr_PortfolioTurnoverHeading

Portfolio Turnover

rr_PortfolioTurnoverRate

90.00%

rr_ExpenseExampleNarrativeTextBlock

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 and then you retain the Shares or redeem all of your Shares at the end of those periods. The example also assumes that your investment has a 5% return each year and that the Fund's net annual operating expenses remain at current levels until November 30, 2013. 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 November 30, 2013. 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, 2013. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

rr_ExpenseExampleNoRedemptionYear03

280

rr_ExpenseExampleNoRedemptionYear10

1,198

rr_StrategyNarrativeTextBlock

The Fund will normally invest at least 90% 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. First Trust will regularly monitor the Fund's tracking accuracy and will seek to maintain an appropriate correlation.

The Index is in the "StrataQuant(R) Series," a family of custom enhanced indices developed, maintained and sponsored by NYSE Euronext or its affiliates ("NYSE Euronext" or an "Index Provider"), and licensed to First Trust Portfolios L.P. by NYSE Group, Inc. ("NYSE Group"), an affiliate of NYSE Euronext. Prior to the acquisition of the American Stock Exchange LLC (the "AMEX") by NYSE Euronext, 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 Euronext to objectively identify and select stocks from the Russell 1000(R) Index in the energy 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, 2012, the Index was comprised of 53 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.

The Fund may lend securities representing up to 20% of the value of its total assets to broker-dealers, banks and other institutions to generate additional income. When the Fund loans its portfolio securities, it will receive, at the inception of each loan, cash collateral equal to at least 102% (for domestic securities) or 105% (for international securities) of the market value of the loaned securities.

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.

MARKET RISK. Market risk is the risk that a particular stock owned by the Fund, Shares of the Fund or stocks in general may fall in value. Shares are subject to market fluctuations caused by such factors as economic, political, regulatory or market developments, changes in interest rates and perceived trends in stock prices. Overall stock values could decline generally or could underperform other investments. Companies with smaller market capitalizations are generally subject to additional market risk.

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. Therefore, the Fund will generally not sell a stock because the stock's issuer is in financial trouble, unless that stock is removed or is anticipated to be removed from the Index.

NON-DIVERSIFICATION RISK. The Fund is classified as "non-diversified" under the Investment Company Act of 1940, as amended (the "1940 Act"). As a result, the Fund is only limited as to the percentage of its assets which may be invested in the securities of any one issuer by the diversification requirements imposed by the Internal Revenue Code of 1986, as amended (the "Code"). The Fund may invest a relatively high percentage of its assets in a limited number of issuers.

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

ENERGY SECTOR RISK. The Fund invests in the securities of companies in the energy sector. The companies in the energy sector 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 issuers in the energy sector 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 have been extremely volatile.

SECURITIES LENDING RISK. The Fund may engage in securities lending. Securities lending involves the risk that the Fund may lose money because the borrower of the Fund's loaned securities fails to return the securities in a timely manner or at all. The Fund could also lose money in the event of a decline in the value of the collateral provided for the loaned securities or a decline in the value of any investments made with cash collateral. These events could also trigger adverse tax consequences for the Fund.

rr_PerformanceNarrativeTextBlock

The bar chart and table below illustrate the annual calendar year returns of the Fund based on NAV for the past four years as well as the average annual Fund and Index returns for the one year and since inception periods ended December 31, 2011. 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 NAV compare to those of the Index, a broad-based market index and two specialized securities market indices. With respect to the Russell 1000(R) Energy 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. In addition to the implementation of the RGS, Russell combined the Russell 1000(R) Integrated Oils Index and the Russell 1000(R) Other Energy Index into one index, the Russell 1000(R) Energy Index. Consequently, performance data is not available for the Russell 1000(R) Energy Index for the entire "Since Inception" period 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_AnnualReturn2008

(50.78%)

rr_AnnualReturn2010

27.77%

rr_BarChartFootnotesTextBlock

The Fund's year-to-date return based on NAV for the period 12/31/2011 to 9/30/2012 was 1.52%.

rr_PerformanceTableHeading

Average Annual Total Returns for the Periods Ended December 31, 2011

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear01

(8.16%)

rr_AverageAnnualReturnInceptionDate

May 08, 2007

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear01

(8.30%)

rr_AverageAnnualReturnInceptionDate

May 08, 2007

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear01

(5.30%)

rr_AverageAnnualReturnInceptionDate

May 08, 2007

rr_RiskReturnAbstract

rr_AverageAnnualReturnSinceInception

(1.54%)

rr_AverageAnnualReturnYear01

(7.49%)

rr_AverageAnnualReturnInceptionDate

May 08, 2007

rr_RiskReturnAbstract

rr_AverageAnnualReturnSinceInception

2.92%

rr_AverageAnnualReturnYear01

3.43%

rr_AverageAnnualReturnInceptionDate

May 08, 2007

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_OperatingExpensesCaption

Annual Fund Operating Expenses (Expenses that you pay each year as a percentage of the value of your investment)

rr_DistributionAndService12b1FeesOverAssets

none

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

rr_ExpensesOverAssets

0.74%

rr_NetExpensesOverAssets

0.70%

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 93% of the average value of its portfolio.

rr_ExpenseExampleHeading

Example

rr_ExpenseExampleNoRedemptionYear01

72

rr_ExpenseExampleNoRedemptionYear05

509

rr_StrategyHeading

Principal Investment Strategies

rr_RiskHeading

Principal Risks

rr_BarChartAndPerformanceTableHeading

Annual Total Return

rr_BarChartHeading

Calendar Year Total Returns as of 12/31

rr_AnnualReturn2009

31.65%

rr_AnnualReturn2011

(7.36%)

rr_BarChartClosingTextBlock

During the four-year period ended December 31, 2011, the Fund's highest and lowest calendar quarter returns were 30.65% and -22.64%, respectively, for the quarters ended June 30, 2009 and March 31, 2009. The Fund's past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future.

rr_AverageAnnualReturnLabel

Return Before Taxes

rr_AverageAnnualReturnSinceInception

(6.92%)

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions

rr_AverageAnnualReturnSinceInception

(7.50%)

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions and Sale of Shares

rr_AverageAnnualReturnSinceInception

(6.08%)

rr_AverageAnnualReturnYear01

1.50%

rr_AverageAnnualReturnInceptionDate

May 08, 2007

rr_RiskReturnAbstract

rr_AverageAnnualReturnSinceInception

(6.03%)

rr_AverageAnnualReturnYear01

(17.06%)

rr_AverageAnnualReturnInceptionDate

May 08, 2007

rr_RiskReturnAbstract

rr_AverageAnnualReturnSinceInception

none

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").

Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of Offering Price)

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.

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

rr_ManagementFeesOverAssets

0.50%

rr_OtherExpensesOverAssets

0.23%

rr_FeeWaiverOrReimbursementOverAssets

(0.03%)

^[1]

rr_PortfolioTurnoverHeading

Portfolio Turnover

rr_PortfolioTurnoverRate

109.00%

rr_ExpenseExampleNarrativeTextBlock

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 and then you retain the Shares or redeem all of your Shares at the end of those periods. The example also assumes that your investment has a 5% return each year and that the Fund's net annual operating expenses remain at current levels until November 30, 2013. 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 November 30, 2013. 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, 2013. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

rr_ExpenseExampleNoRedemptionYear03

274

rr_ExpenseExampleNoRedemptionYear10

1,167

rr_StrategyNarrativeTextBlock

The Fund will normally invest at least 90% 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. First Trust will regularly monitor the Fund's tracking accuracy and will seek to maintain an appropriate correlation.

The Index is in the "StrataQuant(R) Series," a family of custom enhanced indices developed, maintained and sponsored by NYSE Euronext or its affiliates ("NYSE Euronext" or an "Index Provider"), and licensed to First Trust Portfolios L.P. by NYSE Group, Inc. ("NYSE Group"), an affiliate of NYSE Euronext. Prior to the acquisition of the American Stock Exchange LLC (the "AMEX") by NYSE Euronext, 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 Euronext 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, 2012, the Index was comprised of 72 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.

MARKET RISK. Market risk is the risk that a particular stock owned by the Fund, Shares of the Fund or stocks in general may fall in value. Shares are subject to market fluctuations caused by such factors as economic, political, regulatory or market developments, changes in interest rates and perceived trends in stock prices. Overall stock values could decline generally or could underperform other investments. Companies with smaller market capitalizations are generally subject to additional market risk.

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. Therefore, the Fund will generally not sell a stock because the stock's issuer is in financial trouble, unless that stock is removed or is anticipated to be removed from the Index.

NON-DIVERSIFICATION RISK. The Fund is classified as "non-diversified" under the Investment Company Act of 1940, as amended (the "1940 Act"). As a result, the Fund is only limited as to the percentage of its assets which may be invested in the securities of any one issuer by the diversification requirements imposed by the Internal Revenue Code of 1986, as amended (the "Code"). The Fund may invest a relatively high percentage of its assets in a limited number of issuers.

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

HEALTH CARE SECTOR RISK. The Fund invests in the securities of companies in the health care sector. Companies in the health care sector are involved in medical services or health care, including biotechnology research and production, drugs and pharmaceuticals and health care facilities and services, and 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.

rr_PerformanceNarrativeTextBlock

The bar chart and table below illustrate the annual calendar year returns of the Fund based on NAV for the past four years as well as the average annual Fund and Index returns for the one year and since inception periods ended December 31, 2011. 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 NAV 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 "Since Inception" period 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_AnnualReturn2008

(29.32%)

rr_AnnualReturn2010

19.04%

rr_BarChartFootnotesTextBlock

The Fund's year-to-date return based on NAV for the period 12/31/2011 to 9/30/2012 was 21.06%.

rr_PerformanceTableHeading

Average Annual Total Returns for the Periods Ended December 31, 2011

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear01

5.76%

rr_AverageAnnualReturnInceptionDate

May 08, 2007

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear01

5.72%

rr_AverageAnnualReturnInceptionDate

May 08, 2007

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear01

3.75%

rr_AverageAnnualReturnInceptionDate

May 08, 2007

rr_RiskReturnAbstract

rr_AverageAnnualReturnSinceInception

(1.54%)

rr_AverageAnnualReturnYear01

6.56%

rr_AverageAnnualReturnInceptionDate

May 08, 2007

rr_RiskReturnAbstract

rr_AverageAnnualReturnSinceInception

0.92%

rr_AverageAnnualReturnYear01

11.78%

rr_AverageAnnualReturnInceptionDate

May 08, 2007

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_OperatingExpensesCaption

Annual Fund Operating Expenses (Expenses that you pay each year as a percentage of the value of your investment)

rr_DistributionAndService12b1FeesOverAssets

none

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

rr_ExpensesOverAssets

0.78%

rr_NetExpensesOverAssets

0.70%

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 97% of the average value of its portfolio.

rr_ExpenseExampleHeading

Example

rr_ExpenseExampleNoRedemptionYear01

72

rr_ExpenseExampleNoRedemptionYear05

525

rr_StrategyHeading

Principal Investment Strategies

rr_RiskHeading

Principal Risks

rr_BarChartAndPerformanceTableHeading

Annual Total Return

rr_BarChartHeading

Calendar Year Total Returns as of 12/31

rr_AnnualReturn2009

42.14%

rr_AnnualReturn2011

(5.95%)

rr_BarChartClosingTextBlock

During the four-year period ended December 31, 2011, 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_AverageAnnualReturnLabel

Return Before Taxes

rr_AverageAnnualReturnSinceInception

(2.62%)

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions

rr_AverageAnnualReturnSinceInception

(2.81%)

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions and Sale of Shares

rr_AverageAnnualReturnSinceInception

(2.33%)

rr_AverageAnnualReturnYear01

1.50%

rr_AverageAnnualReturnInceptionDate

May 08, 2007

rr_RiskReturnAbstract

rr_AverageAnnualReturnSinceInception

(1.87%)

rr_AverageAnnualReturnYear01

(0.59%)

rr_AverageAnnualReturnInceptionDate

May 08, 2007

rr_RiskReturnAbstract

rr_AverageAnnualReturnSinceInception

none

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").

Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of Offering Price)

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.

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

rr_ManagementFeesOverAssets

0.50%

rr_OtherExpensesOverAssets

0.23%

rr_FeeWaiverOrReimbursementOverAssets

(0.03%)

^[1]

rr_PortfolioTurnoverHeading

Portfolio Turnover

rr_PortfolioTurnoverRate

92.00%

rr_ExpenseExampleNarrativeTextBlock

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 and then you retain the Shares or redeem all of your Shares at the end of those periods. The example also assumes that your investment has a 5% return each year and that the Fund's net annual operating expenses remain at current levels until November 30, 2013. 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 November 30, 2013. 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, 2013. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

rr_ExpenseExampleNoRedemptionYear03

274

rr_ExpenseExampleNoRedemptionYear10

1,167

rr_StrategyNarrativeTextBlock

The Fund will normally invest at least 90% 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. First Trust will regularly monitor the Fund's tracking accuracy and will seek to maintain an appropriate correlation.

The Index is in the "StrataQuant(R) Series," a family of custom enhanced indices developed, maintained and sponsored by NYSE Euronext or its affiliates ("NYSE Euronext" or an "Index Provider"), and licensed to First Trust Portfolios L.P. by NYSE Group, Inc. ("NYSE Group"), an affiliate of NYSE Euronext. Prior to the acquisition of the American Stock Exchange LLC (the "AMEX") by NYSE Euronext, 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 Euronext 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, 2012, the Index was comprised of 56 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.

MARKET RISK. Market risk is the risk that a particular stock owned by the Fund, Shares of the Fund or stocks in general may fall in value. Shares are subject to market fluctuations caused by such factors as economic, political, regulatory or market developments, changes in interest rates and perceived trends in stock prices. Overall stock values could decline generally or could underperform other investments. Companies with smaller market capitalizations are generally subject to additional market risk.

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. Therefore, the Fund will generally not sell a stock because the stock's issuer is in financial trouble, unless that stock is removed or is anticipated to be removed from the Index.

NON-DIVERSIFICATION RISK. The Fund is classified as "non-diversified" under the Investment Company Act of 1940, as amended (the "1940 Act"). As a result, the Fund is only limited as to the percentage of its assets which may be invested in the securities of any one issuer by the diversification requirements imposed by the Internal Revenue Code of 1986, as amended (the "Code"). The Fund may invest a relatively high percentage of its assets in a limited number of issuers.

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

MATERIALS AND PROCESSING SECTOR RISK. The Fund invests in the securities of companies in the materials and processing sector. Companies in the materials and processing sector 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.

rr_PerformanceNarrativeTextBlock

The bar chart and table below illustrate the annual calendar year returns of the Fund based on NAV for the past four years as well as the average annual Fund and Index returns for the one year and since inception periods ended December 31, 2011. 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 NAV 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 "Since Inception" period 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_AnnualReturn2008

(44.61%)

rr_AnnualReturn2010

28.15%

rr_BarChartFootnotesTextBlock

The Fund's year-to-date return based on NAV for the period 12/31/2011 to 9/30/2012 was 15.96%.

rr_PerformanceTableHeading

Average Annual Total Returns for the Periods Ended December 31, 2011

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear01

(10.11%)

rr_AverageAnnualReturnInceptionDate

May 08, 2007

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear01

(10.20%)

rr_AverageAnnualReturnInceptionDate

May 08, 2007

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear01

(6.56%)

rr_AverageAnnualReturnInceptionDate

May 08, 2007

rr_RiskReturnAbstract

rr_AverageAnnualReturnSinceInception

(1.54%)

rr_AverageAnnualReturnYear01

(9.26%)

rr_AverageAnnualReturnInceptionDate

May 08, 2007

rr_RiskReturnAbstract

rr_AverageAnnualReturnSinceInception

(1.05%)

rr_AverageAnnualReturnYear01

(7.21%)

rr_AverageAnnualReturnInceptionDate

May 08, 2007

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_OperatingExpensesCaption

Annual Fund Operating Expenses (Expenses that you pay each year as a percentage of the value of your investment)

rr_DistributionAndService12b1FeesOverAssets

none

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

rr_ExpensesOverAssets

0.74%

rr_NetExpensesOverAssets

0.70%

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 101% of the average value of its portfolio.

rr_ExpenseExampleHeading

Example

rr_ExpenseExampleNoRedemptionYear01

72

rr_ExpenseExampleNoRedemptionYear05

509

rr_StrategyHeading

Principal Investment Strategies

rr_RiskHeading

Principal Risks

rr_BarChartAndPerformanceTableHeading

Annual Total Return

rr_BarChartHeading

Calendar Year Total Returns as of 12/31

rr_AnnualReturn2009

66.95%

rr_AnnualReturn2011

(11.65%)

rr_BarChartClosingTextBlock

During the four-year period ended December 31, 2011, 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_AverageAnnualReturnLabel

Return Before Taxes

rr_AverageAnnualReturnSinceInception

0.03%

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions

rr_AverageAnnualReturnSinceInception

0.03%

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions and Sale of Shares

rr_AverageAnnualReturnSinceInception

0.02%

rr_AverageAnnualReturnYear01

1.50%

rr_AverageAnnualReturnInceptionDate

May 08, 2007

rr_RiskReturnAbstract

rr_AverageAnnualReturnSinceInception

0.92%

rr_AverageAnnualReturnYear01

2.41%

rr_AverageAnnualReturnInceptionDate

May 08, 2007

rr_RiskReturnAbstract

rr_AverageAnnualReturnSinceInception

none

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").

Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of Offering Price)

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.

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

rr_ManagementFeesOverAssets

0.50%

rr_OtherExpensesOverAssets

0.22%

rr_FeeWaiverOrReimbursementOverAssets

(0.02%)

^[1]

rr_PortfolioTurnoverHeading

Portfolio Turnover

rr_PortfolioTurnoverRate

72.00%

rr_ExpenseExampleNarrativeTextBlock

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 and then you retain the Shares or redeem all of your Shares at the end of those periods. The example also assumes that your investment has a 5% return each year and that the Fund's net annual operating expenses remain at current levels until November 30, 2013. 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 November 30, 2013. 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, 2013. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

rr_ExpenseExampleNoRedemptionYear03

273

rr_ExpenseExampleNoRedemptionYear10

1,156

rr_StrategyNarrativeTextBlock

The Fund will normally invest at least 90% 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. First Trust will regularly monitor the Fund's tracking accuracy and will seek to maintain an appropriate correlation.

The Index is in the "StrataQuant(R) Series," a family of custom enhanced indices developed, maintained and sponsored by NYSE Euronext or its affiliates ("NYSE Euronext" or an "Index Provider"), and licensed to First Trust Portfolios L.P. by NYSE Group, Inc. ("NYSE Group"), an affiliate of NYSE Euronext. Prior to the acquisition of the American Stock Exchange LLC (the "AMEX") by NYSE Euronext, 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 Euronext 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, 2012, the Index was comprised of 46 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.

MARKET RISK. Market risk is the risk that a particular stock owned by the Fund, Shares of the Fund or stocks in general may fall in value. Shares are subject to market fluctuations caused by such factors as economic, political, regulatory or market developments, changes in interest rates and perceived trends in stock prices. Overall stock values could decline generally or could underperform other investments. Companies with smaller market capitalizations are generally subject to additional market risk.

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. Therefore, the Fund will generally not sell a stock because the stock's issuer is in financial trouble, unless that stock is removed or is anticipated to be removed from the Index.

NON-DIVERSIFICATION RISK. The Fund is classified as "non-diversified" under the Investment Company Act of 1940, as amended (the "1940 Act"). As a result, the Fund is only limited as to the percentage of its assets which may be invested in the securities of any one issuer by the diversification requirements imposed by the Internal Revenue Code of 1986, as amended (the "Code"). The Fund may invest a relatively high percentage of its assets in a limited number of issuers.

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

UTILITIES SECTOR RISK. The Fund invests in the securities of companies in the utilities sector. Issuers in the utilities sector are subject to 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. Utilities issuers have been experiencing certain of these problems to varying degrees.

TELECOMMUNICATIONS SECTOR RISK. The Fund invests in companies in the telecommunications sector. Telecommunications companies are subject to risks, such as: a market characterized by increasing competition and regulation by the Federal Communications Commission and various state regulatory authorities; the need to commit substantial capital to meet increasing competition, particularly in formulating new products and services using new technology; and technological innovations that may make various products and services obsolete.

rr_PerformanceNarrativeTextBlock

The bar chart and table below illustrate the annual calendar year returns of the Fund based on NAV for the past four years as well as the average annual Fund and Index returns for the one year and since inception periods ended December 31, 2011. 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 NAV 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 "Since Inception" period 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_AnnualReturn2008

(27.43%)

rr_AnnualReturn2010

10.54%

rr_BarChartFootnotesTextBlock

The Fund's year-to-date return based on NAV for the period 12/31/2011 to 9/30/2012 was 8.12%.

rr_PerformanceTableHeading

Average Annual Total Returns for the Periods Ended December 31, 2011

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear01

10.33%

rr_AverageAnnualReturnInceptionDate

May 08, 2007

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear01

9.63%

rr_AverageAnnualReturnInceptionDate

May 08, 2007

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear01

6.71%

rr_AverageAnnualReturnInceptionDate

May 08, 2007

rr_RiskReturnAbstract

rr_AverageAnnualReturnSinceInception

(1.54%)

rr_AverageAnnualReturnYear01

11.23%

rr_AverageAnnualReturnInceptionDate

May 08, 2007

rr_RiskReturnAbstract

rr_AverageAnnualReturnSinceInception

0.73%

rr_AverageAnnualReturnYear01

12.58%

rr_AverageAnnualReturnInceptionDate

May 08, 2007

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_OperatingExpensesCaption

Annual Fund Operating Expenses (Expenses that you pay each year as a percentage of the value of your investment)

rr_DistributionAndService12b1FeesOverAssets

none

rr_OtherExpensesOverAssets

0.17%

rr_FeeWaiverOrReimbursementOverAssets

none

^[1]

rr_PortfolioTurnoverHeading

Portfolio Turnover

rr_PortfolioTurnoverRate

95.00%

rr_ExpenseExampleNarrativeTextBlock

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 and then you retain the Shares or sell all of your Shares at the end of those periods. The example also assumes that your investment has a 5% return each year and that the Fund's annual 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 November 30, 2013. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

rr_ExpenseExampleNoRedemptionYear03

269

rr_ExpenseExampleNoRedemptionYear10

1,135

rr_StrategyNarrativeTextBlock

The Fund will normally invest at least 90% 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. First Trust will regularly monitor the Fund's tracking accuracy and will seek to maintain an appropriate 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) 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, 2012, the Index was comprised of 374 stocks and the market capitalization range represented in the Index was $1.2 billion to $572.5 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.

MARKET RISK. Market risk is the risk that a particular stock owned by the Fund, Shares of the Fund or stocks in general may fall in value. Shares are subject to market fluctuations caused by such factors as economic, political, regulatory or market developments, changes in interest rates and perceived trends in stock prices. Overall stock 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. Therefore, the Fund will generally not sell a stock because the stock's issuer is in financial trouble, unless that stock is removed or is anticipated to be removed from the Index.

NON-DIVERSIFICATION RISK. The Fund is classified as "non-diversified" under the Investment Company Act of 1940, as amended (the "1940 Act"). As a result, the Fund is only limited as to the percentage of its assets which may be invested in the securities of any one issuer by the diversification requirements imposed by the Internal Revenue Code of 1986, as amended (the "Code"). The Fund may invest a relatively high percentage of its assets in a limited number of issuers.

INDEX TRACKING RISK. You should anticipate that the value of Fund Shares will decline, more or less, in correlation with any decline in the value of that 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. For purposes of determining the market capitalization range of such securities, the Fund will use the current range of the Index. However, the Fund will not be forced to sell a stock because the stock 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.

rr_PerformanceNarrativeTextBlock

The bar chart and table below illustrate the annual calendar year returns of the Fund based on NAV for the past four years as well as the average annual Fund and Index returns for the one year and since inception periods ended December 31, 2011. 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 NAV 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_AnnualReturn2008

(38.35%)

rr_AnnualReturn2010

20.66%

rr_BarChartFootnotesTextBlock

The Fund's year-to-date return based on NAV for the period 12/31/2011 to 9/30/2012 was 11.45%.

rr_PerformanceTableHeading

Average Annual Total Returns for the Periods Ended December 31, 2011

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear01

(0.22%)

rr_AverageAnnualReturnInceptionDate

May 08, 2007

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear01

(0.59%)

rr_AverageAnnualReturnInceptionDate

May 08, 2007

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear01

(0.14%)

rr_AverageAnnualReturnInceptionDate

May 08, 2007

rr_RiskReturnAbstract

rr_AverageAnnualReturnSinceInception

(0.26%)

rr_AverageAnnualReturnYear01

2.11%

rr_AverageAnnualReturnInceptionDate

May 08, 2007

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_OperatingExpensesCaption

Annual Fund Operating Expenses (Expenses that you pay each year as a percentage of the value of your investment)

rr_DistributionAndService12b1FeesOverAssets

none

rr_OtherExpensesOverAssets

0.17%

rr_FeeWaiverOrReimbursementOverAssets

none

^[1]

rr_PortfolioTurnoverHeading

Portfolio Turnover

rr_PortfolioTurnoverRate

94.00%

rr_ExpenseExampleNarrativeTextBlock

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 and then you retain the Shares or sell all of your Shares at the end of those periods. The example also assumes that your investment has a 5% return each year and that the Fund's annual 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 November 30, 2013. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

rr_ExpenseExampleNoRedemptionYear03

269

rr_ExpenseExampleNoRedemptionYear10

1,135

rr_StrategyNarrativeTextBlock

The Fund will normally invest at least 90% 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. First Trust will regularly monitor the Fund's tracking accuracy and will seek to maintain an appropriate 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. As of July 31, 2012, the Index was comprised of 299 stocks and the market capitalization range represented in the Index was $289 million to $12.8 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.

The Fund may lend securities representing up to 20% of the value of its total assets to broker-dealers, banks and other institutions to generate additional income. When the Fund loans its portfolio securities, it will receive, at the inception of each loan, cash collateral equal to at least 102% (for domestic securities) or 105% (for international securities) of the market value of the loaned securities.

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.

MARKET RISK. Market risk is the risk that a particular stock owned by the Fund, Shares of the Fund or stocks in general may fall in value. Shares are subject to market fluctuations caused by such factors as economic, political, regulatory or market developments, changes in interest rates and perceived trends in stock prices. Overall stock values could decline generally or could underperform other investments. Companies with smaller market capitalizations are generally subject to additional market risk.

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. Therefore, the Fund will generally not sell a stock because the stock's issuer is in financial trouble, unless that stock is removed or is anticipated to be removed from the Index.

NON-DIVERSIFICATION RISK. The Fund is classified as "non-diversified" under the Investment Company Act of 1940, as amended (the "1940 Act"). As a result, the Fund is only limited as to the percentage of its assets which may be invested in the securities of any one issuer by the diversification requirements imposed by the Internal Revenue Code of 1986, as amended (the "Code"). The Fund may invest a relatively high percentage of its assets in a limited number of issuers.

INDEX TRACKING RISK. You should anticipate that the value of Fund Shares will decline, more or less, in correlation with any decline in the value of that 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. For purposes of determining the market capitalization range of such securities, the Fund will use the current range of the Index. However, the Fund will not be forced to sell a stock because the stock 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.

SMALLER COMPANY 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.

SECURITIES LENDING RISK. The Fund may engage in securities lending. Securities lending involves the risk that the Fund may lose money because the borrower of the Fund's loaned securities fails to return the securities in a timely manner or at all. The Fund could also lose money in the event of a decline in the value of the collateral provided for the loaned securities or a decline in the value of any investments made with cash collateral. These events could also trigger adverse tax consequences for the Fund.

rr_PerformanceNarrativeTextBlock

The bar chart and table below illustrate the annual calendar year returns of the Fund based on NAV for the past four years as well as the average annual Fund and Index returns for the one year and since inception periods ended December 31, 2011. 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 NAV 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_AnnualReturn2008

(36.77%)

rr_AnnualReturn2010

27.03%

rr_BarChartFootnotesTextBlock

The Fund's year-to-date return based on NAV for the period 12/31/2011 to 9/30/2012 was 10.04%.

rr_PerformanceTableHeading

Average Annual Total Returns for the Periods Ended December 31, 2011

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear01

0.83%

rr_AverageAnnualReturnInceptionDate

May 08, 2007

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear01

0.66%

rr_AverageAnnualReturnInceptionDate

May 08, 2007

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear01

0.55%

rr_AverageAnnualReturnInceptionDate

May 08, 2007

rr_RiskReturnAbstract

rr_AverageAnnualReturnSinceInception

3.25%

rr_AverageAnnualReturnYear01

(1.73%)

rr_AverageAnnualReturnInceptionDate

May 08, 2007

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_OperatingExpensesCaption

Annual Fund Operating Expenses (Expenses that you pay each year as a percentage of the value of your investment)

rr_DistributionAndService12b1FeesOverAssets

none

rr_OtherExpensesOverAssets

0.19%

rr_FeeWaiverOrReimbursementOverAssets

none

^[1]

rr_PortfolioTurnoverHeading

Portfolio Turnover

rr_PortfolioTurnoverRate

101.00%

rr_ExpenseExampleNarrativeTextBlock

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 and then you retain the Shares or sell all of your Shares at the end of those periods. The example also assumes that your investment has a 5% return each year and that the Fund's annual 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 November 30, 2013. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

rr_ExpenseExampleNoRedemptionYear03

269

rr_ExpenseExampleNoRedemptionYear10

1,135

rr_StrategyNarrativeTextBlock

The Fund will normally invest at least 90% 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. First Trust will regularly monitor the Fund's tracking accuracy and will seek to maintain an appropriate 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. As of July 31, 2012, the Index was comprised of 450 stocks and the market capitalization range represented in the Index was $80 million to $3.2 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.

The Fund may lend securities representing up to 20% of the value of its total assets to broker-dealers, banks and other institutions to generate additional income. When the Fund loans its portfolio securities, it will receive, at the inception of each loan, cash collateral equal to at least 102% (for domestic securities) or 105% (for international securities) of the market value of the loaned securities.

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.

MARKET RISK. Market risk is the risk that a particular stock owned by the Fund, Shares of the Fund or stocks in general may fall in value. Shares are subject to market fluctuations caused by such factors as economic, political, regulatory or market developments, changes in interest rates and perceived trends in stock prices. Overall stock values could decline generally or could underperform other investments. Companies with smaller market capitalizations are generally subject to additional market risk.

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. Therefore, the Fund will generally not sell a stock because the stock's issuer is in financial trouble, unless that stock is removed or is anticipated to be removed from the Index.

NON-DIVERSIFICATION RISK. The Fund is classified as "non-diversified" under the Investment Company Act of 1940, as amended (the "1940 Act"). As a result, the Fund is only limited as to the percentage of its assets which may be invested in the securities of any one issuer by the diversification requirements imposed by the Internal Revenue Code of 1986, as amended (the "Code"). The Fund may invest a relatively high percentage of its assets in a limited number of issuers.

INDEX TRACKING RISK. You should anticipate that the value of Fund Shares will decline, more or less, in correlation with any decline in the value of that 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. For purposes of determining the market capitalization range of such securities, the Fund will use the current range of the Index. However, the Fund will not be forced to sell a stock because the stock 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.

SMALLER COMPANY 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.

SECURITIES LENDING RISK. The Fund may engage in securities lending. Securities lending involves the risk that the Fund may lose money because the borrower of the Fund's loaned securities fails to return the securities in a timely manner or at all. The Fund could also lose money in the event of a decline in the value of the collateral provided for the loaned securities or a decline in the value of any investments made with cash collateral. These events could also trigger adverse tax consequences for the Fund.

rr_PerformanceNarrativeTextBlock

The bar chart and table below illustrate the annual calendar year returns of the Fund based on NAV for the past four years as well as the average annual Fund and Index returns for the one year and since inception periods ended December 31, 2011. 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 NAV 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_AnnualReturn2008

(34.28%)

rr_AnnualReturn2010

26.92%

rr_BarChartFootnotesTextBlock

The Fund's year-to-date return based on NAV for the period 12/31/2011 to 9/30/2012 was 12.75%.

rr_PerformanceTableHeading

Average Annual Total Returns for the Periods Ended December 31, 2011

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear01

(0.10%)

rr_AverageAnnualReturnInceptionDate

May 08, 2007

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear01

(0.17%)

rr_AverageAnnualReturnInceptionDate

May 08, 2007

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear01

(0.07%)

rr_AverageAnnualReturnInceptionDate

May 08, 2007

rr_RiskReturnAbstract

rr_AverageAnnualReturnSinceInception

1.12%

rr_AverageAnnualReturnYear01

1.02%

rr_AverageAnnualReturnInceptionDate

May 08, 2007

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_OperatingExpensesCaption

Annual Fund Operating Expenses (Expenses that you pay each year as a percentage of the value of your investment)

rr_DistributionAndService12b1FeesOverAssets

none

rr_OtherExpensesOverAssets

0.18%

rr_FeeWaiverOrReimbursementOverAssets

none

^[1]

rr_PortfolioTurnoverHeading

Portfolio Turnover

rr_PortfolioTurnoverRate

88.00%

rr_ExpenseExampleNarrativeTextBlock

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 and then you retain the Shares or sell all of your Shares at the end of those periods. The example also assumes that your investment has a 5% return each year and that the Fund's annual 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 November 30, 2013. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

rr_ExpenseExampleNoRedemptionYear03

269

rr_ExpenseExampleNoRedemptionYear10

1,135

rr_StrategyNarrativeTextBlock

The Fund will normally invest at least 90% 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. First Trust will regularly monitor the Fund's tracking accuracy and will seek to maintain an appropriate 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, 2012, the Index was comprised of 213 stocks and the market capitalization range represented in the Index was $1.2 billion to $406.1 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.

MARKET RISK. Market risk is the risk that a particular stock owned by the Fund, Shares of the Fund or stocks in general may fall in value. Shares are subject to market fluctuations caused by such factors as economic, political, regulatory or market developments, changes in interest rates and perceived trends in stock prices. Overall stock 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. Therefore, the Fund will generally not sell a stock because the stock's issuer is in financial trouble, unless that stock is removed or is anticipated to be removed from the Index.

NON-DIVERSIFICATION RISK. The Fund is classified as "non-diversified" under the Investment Company Act of 1940, as amended (the "1940 Act"). As a result, the Fund is only limited as to the percentage of its assets which may be invested in the securities of any one issuer by the diversification requirements imposed by the Internal Revenue Code of 1986, as amended (the "Code"). The Fund may invest a relatively high percentage of its assets in a limited number of issuers.

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

VALUE INVESTMENT STYLE RISK. Value companies may have experienced 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.

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. For purposes of determining the market capitalization range of such securities, the Fund will use the current range of the Index. However, the Fund will not be forced to sell a stock because the stock 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.

rr_PerformanceNarrativeTextBlock

The bar chart and table below illustrate the annual calendar year returns of the Fund based on NAV for the past four years as well as the average annual Fund and Index returns for the one year and since inception periods ended December 31, 2011. 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 NAV 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_AnnualReturn2008

(36.09%)

rr_AnnualReturn2010

18.55%

rr_BarChartFootnotesTextBlock

The Fund's year-to-date return based on NAV for the period 12/31/2011 to 9/30/2012 was 13.48%.

rr_PerformanceTableHeading

Average Annual Total Returns for the Periods Ended December 31, 2011

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear01

1.32%

rr_AverageAnnualReturnInceptionDate

May 08, 2007

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear01

0.83%

rr_AverageAnnualReturnInceptionDate

May 08, 2007

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear01

0.87%

rr_AverageAnnualReturnInceptionDate

May 08, 2007

rr_RiskReturnAbstract

rr_AverageAnnualReturnSinceInception

(1.70%)

rr_AverageAnnualReturnYear01

2.12%

^[2]

rr_AverageAnnualReturnInceptionDate

May 08, 2007

rr_RiskReturnAbstract

rr_AverageAnnualReturnSinceInception

(4.70%)

rr_RiskReturnHeading

SUMMARY INFORMATION

rr_ObjectivePrimaryTextBlock

The First Trust Large Cap Growth AlphaDEX(R) Fund (the "Fund") (formerly, First Trust Large Cap Growth Opportunities AlphaDEX(R) 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 Growth Index (the "Index") (formerly, Defined Large Cap Growth Opportunities Index).

Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of Offering Price)

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.

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Fees Previously Waived or Expenses Reimbursed by First Trust

rr_ManagementFeesOverAssets

0.50%

rr_Component1OtherExpensesOverAssets

0.01%

^[1]

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

rr_ExpensesOverAssets

0.70%

rr_NetExpensesOverAssets

0.70%

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 162% of the average value of its portfolio.

rr_ExpenseExampleHeading

Example

rr_ExpenseExampleNoRedemptionYear01

72

rr_ExpenseExampleNoRedemptionYear05

493

rr_StrategyHeading

Principal Investment Strategies

rr_RiskHeading

Principal Risks

rr_BarChartAndPerformanceTableHeading

Annual Total Return

rr_BarChartHeading

Calendar Year Total Returns as of 12/31

rr_AnnualReturn2009

29.33%

rr_AnnualReturn2011

(2.65%)

rr_BarChartClosingTextBlock

During the four-year period ended December 31, 2011, 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.

rr_AverageAnnualReturnLabel

Return Before Taxes

rr_AverageAnnualReturnSinceInception

(1.31%)

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions

rr_AverageAnnualReturnSinceInception

(1.50%)

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions and Sale of Shares

rr_AverageAnnualReturnSinceInception

(1.22%)

rr_AverageAnnualReturnYear01

2.11%

rr_AverageAnnualReturnInceptionDate

May 08, 2007

rr_RiskReturnAbstract

rr_AverageAnnualReturnSinceInception

(0.57%)

^[3]

rr_AverageAnnualReturnYear01

4.65%

rr_AverageAnnualReturnInceptionDate

May 08, 2007

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_OperatingExpensesCaption

Annual Fund Operating Expenses (Expenses that you pay each year as a percentage of the value of your investment)

rr_DistributionAndService12b1FeesOverAssets

none

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

rr_ExpensesOverAssets

0.80%

rr_NetExpensesOverAssets

0.70%

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 90% of the average value of its portfolio.

rr_ExpenseExampleHeading

Example

rr_ExpenseExampleNoRedemptionYear01

72

rr_ExpenseExampleNoRedemptionYear05

533

rr_StrategyHeading

Principal Investment Strategies

rr_RiskHeading

Principal Risks

rr_BarChartAndPerformanceTableHeading

Annual Total Return

rr_BarChartHeading

Calendar Year Total Returns as of 12/31

rr_AnnualReturn2009

47.57%

rr_AnnualReturn2011

0.57%

rr_BarChartClosingTextBlock

During the four-year period ended December 31, 2011, the Fund's highest and lowest calendar quarter returns were 33.70% and -26.85%, 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_AverageAnnualReturnLabel

Return Before Taxes

rr_AverageAnnualReturnSinceInception

0.24%

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions

rr_AverageAnnualReturnSinceInception

(0.26%)

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions and Sale of Shares

rr_AverageAnnualReturnSinceInception

(0.11%)

rr_AverageAnnualReturnYear01

1.34%

rr_AverageAnnualReturnInceptionDate

May 08, 2007

rr_RiskReturnAbstract

rr_AverageAnnualReturnSinceInception

(1.39%)

rr_AverageAnnualReturnYear01

(0.69%)

rr_AverageAnnualReturnInceptionDate

May 08, 2007

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_OperatingExpensesCaption

Annual Fund Operating Expenses (Expenses that you pay each year as a percentage of the value of your investment)

rr_DistributionAndService12b1FeesOverAssets

none

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

rr_ExpensesOverAssets

0.85%

rr_NetExpensesOverAssets

0.70%

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 155% of the average value of its portfolio.

rr_ExpenseExampleHeading

Example

rr_ExpenseExampleNoRedemptionYear01

72

rr_ExpenseExampleNoRedemptionYear05

554

rr_StrategyHeading

Principal Investment Strategies

rr_RiskHeading

Principal Risks

rr_BarChartAndPerformanceTableHeading

Annual Total Return

rr_BarChartHeading

Calendar Year Total Returns as of 12/31

rr_AnnualReturn2009

29.69%

rr_AnnualReturn2011

(0.59%)

rr_BarChartClosingTextBlock

During the four-year period ended December 31, 2011, the Fund's highest and lowest calendar quarter returns were 19.09% and -23.61%, 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_AverageAnnualReturnLabel

Return Before Taxes

rr_AverageAnnualReturnSinceInception

0.14%

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions

rr_AverageAnnualReturnSinceInception

0.05%

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions and Sale of Shares

rr_AverageAnnualReturnSinceInception

0.07%

rr_AverageAnnualReturnYear01

1.75%

rr_AverageAnnualReturnInceptionDate

May 08, 2007

rr_RiskReturnAbstract

rr_AverageAnnualReturnSinceInception

0.91%

rr_AverageAnnualReturnYear01

4.17%

rr_AverageAnnualReturnInceptionDate

May 08, 2007

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_OperatingExpensesCaption

Annual Fund Operating Expenses (Expenses that you pay each year as a percentage of the value of your investment)

rr_DistributionAndService12b1FeesOverAssets

none

rr_ExpensesOverAssets

0.70%

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_ExpenseExampleHeading

Example

rr_ExpenseExampleNoRedemptionYear01

72

rr_ExpenseExampleNoRedemptionYear05

493

rr_StrategyHeading

Principal Investment Strategies

rr_RiskHeading

Principal Risks

rr_BarChartAndPerformanceTableHeading

Annual Total Return

rr_RiskReturnHeading

SUMMARY INFORMATION

rr_ObjectivePrimaryTextBlock

The First Trust Mid Cap Growth 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 Growth Index (the "Index").

Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of Offering Price)

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.

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

rr_ManagementFeesOverAssets

0.70%

rr_OtherExpensesOverAssets

none

rr_PortfolioTurnoverHeading

Portfolio Turnover

rr_PortfolioTurnoverRate

166.00%

rr_ExpenseExampleNarrativeTextBlock

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 and then you retain the Shares or redeem all of your Shares at the end of those periods. The example also assumes that your investment has a 5% return each year and that the Fund's net 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 November 30, 2013. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

rr_ExpenseExampleNoRedemptionYear03

269

rr_ExpenseExampleNoRedemptionYear10

1,135

rr_StrategyNarrativeTextBlock

The Fund will normally invest at least 90% 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. First Trust will regularly monitor the Fund's tracking accuracy and will seek to maintain an appropriate 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) Growth 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, 2012, the Index was comprised of 129 securities and the market capitalization range represented in the Index was $862 million to $12.8 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.

MARKET RISK. Market risk is the risk that a particular stock owned by the Fund, Shares of the Fund or stocks in general may fall in value. Shares are subject to market fluctuations caused by such factors as economic, political, regulatory or market developments, changes in interest rates and perceived trends in stock prices. Overall stock values could decline generally or could underperform other investments. Companies with smaller market capitalizations are generally subject to additional market risk.

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. Therefore, the Fund will generally not sell a stock because the stock's issuer is in financial trouble, unless that stock is removed or is anticipated to be removed from the Index.

NON-DIVERSIFICATION RISK. The Fund is classified as "non-diversified" under the Investment Company Act of 1940, as amended (the "1940 Act"). As a result, the Fund is only limited as to the percentage of its assets which may be invested in the securities of any one issuer by the diversification requirements imposed by the Internal Revenue Code of 1986, as amended (the "Code"). The Fund may invest a relatively high percentage of its assets in a limited number of issuers.

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

GROWTH INVESTMENT STYLE RISK. Securities of growth companies may experience significant fluctuations in price in response to economic, political, regulatory, company specific, sector or market developments, changes in perceptions or interest rate changes.

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. For purposes of determining the market capitalization range of such securities, the Fund will use the current range of the Index. However, the Fund will not be forced to sell a stock because the stock 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.

SMALLER COMPANY RISK. The Fund may invest 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 Fund has not yet operated for a full calendar year and, therefore, performance information is not included in this section of the Prospectus. See "Total Return Information" for performance information regarding the Fund.

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_OperatingExpensesCaption

Annual Fund Operating Expenses (Expenses that you pay each year as a percentage of the value of your investment)

rr_DistributionAndService12b1FeesOverAssets

none

rr_ExpensesOverAssets

0.70%

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 103% of the average value of its portfolio.

rr_ExpenseExampleHeading

Example

rr_ExpenseExampleNoRedemptionYear01

72

rr_ExpenseExampleNoRedemptionYear05

493

rr_StrategyHeading

Principal Investment Strategies

rr_RiskHeading

Principal Risks

rr_BarChartAndPerformanceTableHeading

Annual Total Return

rr_RiskReturnHeading

SUMMARY INFORMATION

rr_ObjectivePrimaryTextBlock

The First Trust Small Cap Growth 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 Growth Index (the "Index").

Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of Offering Price)

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.

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

rr_ManagementFeesOverAssets

0.70%

rr_OtherExpensesOverAssets

none

rr_PortfolioTurnoverHeading

Portfolio Turnover

rr_PortfolioTurnoverRate

162.00%

rr_ExpenseExampleNarrativeTextBlock

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 and then you retain the Shares or redeem all of your Shares at the end of those periods. The example also assumes that your investment has a 5% return each year and that the Fund's net 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 November 30, 2013. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

rr_ExpenseExampleNoRedemptionYear03

269

rr_ExpenseExampleNoRedemptionYear10

1,135