v3.26.1
Shareholder Report
6 Months Ended
Jun. 30, 2026
USD ($)
Holding
Shareholder Report [Line Items]  
Document Type N-CSRS
Amendment Flag false
Registrant Name FIRST TRUST EXCHANGE-TRADED ALPHADEX FUND II
Entity Central Index Key 0001510337
Entity Investment Company Type N-1A
Document Period End Date Jun. 30, 2026
C000099049 [Member]  
Shareholder Report [Line Items]  
Fund Name First Trust Emerging Markets AlphaDEX® Fund
Class Name First Trust Emerging Markets AlphaDEX® Fund
Trading Symbol FEM
Security Exchange Name NASDAQ
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about the First Trust Emerging Markets AlphaDEX® Fund (the “Fund”) for the period of January 1, 2026 to June 30, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the Fund at www.ftportfolios.com/fund-documents/etf/FEM. You can also request this information by contacting us at 1-800-621-1675 or info@ftportfolios.com.
Additional Information Phone Number 1-800-621-1675
Additional Information Email info@ftportfolios.com
Additional Information Website www.ftportfolios.com/fund-documents/etf/FEM
Expenses [Text Block]
WHAT WERE THE FUND COSTS FOR THE LAST SIX MONTHS?
(Based on a hypothetical $10,000 investment)
Fund Costs of a $10,000 investment Costs paid as a percentage
of a $10,000 investment
First Trust Emerging Markets AlphaDEX® Fund $43 0.80%(1)
(1)
Annualized.
Expenses Paid, Amount $ 43
Expense Ratio, Percent 0.80% [1]
Net Assets $ 747,031,083
Holdings Count | Holding 159
Investment Company Portfolio Turnover 61.00%
Additional Fund Statistics [Text Block]
KEY FUND STATISTICS (As of June 30, 2026)
Fund net assets $747,031,083
Total number of portfolio holdings 159
Portfolio turnover rate 61%
Holdings [Text Block]
WHAT DID THE FUND INVEST IN? (As of June 30, 2026)
The tables below show the investment makeup of the Fund, representing the percentage of total investments (excluding repurchase agreements held as collateral for securities lending arrangements) of the Fund.
Top Ten Holdings
Kinsus Interconnect Technology Corp. 2.9%
Innolux Corp. 2.4%
Unimicron Technology Corp. 2.0%
Destek Finans Faktoring A/S 1.9%
Nan Ya Printed Circuit Board Corp. 1.9%
Elite Material Co., Ltd. 1.7%
Accton Technology Corp. 1.7%
Eva Airways Corp. 1.4%
Asia Vital Components Co., Ltd. 1.3%
Weichai Power Co., Ltd., Class H 1.3%
Sector Allocation
Graphical Representation - Allocation 2 Chart
Largest Holdings [Text Block]
Top Ten Holdings
Kinsus Interconnect Technology Corp. 2.9%
Innolux Corp. 2.4%
Unimicron Technology Corp. 2.0%
Destek Finans Faktoring A/S 1.9%
Nan Ya Printed Circuit Board Corp. 1.9%
Elite Material Co., Ltd. 1.7%
Accton Technology Corp. 1.7%
Eva Airways Corp. 1.4%
Asia Vital Components Co., Ltd. 1.3%
Weichai Power Co., Ltd., Class H 1.3%
C000099050 [Member]  
Shareholder Report [Line Items]  
Fund Name First Trust Europe AlphaDEX® Fund
Class Name First Trust Europe AlphaDEX® Fund
Trading Symbol FEP
Security Exchange Name NASDAQ
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about the First Trust Europe AlphaDEX® Fund (the “Fund”) for the period of January 1, 2026 to June 30, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the Fund at www.ftportfolios.com/fund-documents/etf/FEP. You can also request this information by contacting us at 1-800-621-1675 or info@ftportfolios.com.
Additional Information Phone Number 1-800-621-1675
Additional Information Email info@ftportfolios.com
Additional Information Website www.ftportfolios.com/fund-documents/etf/FEP
Expenses [Text Block]
WHAT WERE THE FUND COSTS FOR THE LAST SIX MONTHS?
(Based on a hypothetical $10,000 investment)
Fund Costs of a $10,000 investment Costs paid as a percentage
of a $10,000 investment
First Trust Europe AlphaDEX® Fund $41 0.80%(1)
(1)
Annualized.
Expenses Paid, Amount $ 41
Expense Ratio, Percent 0.80% [2]
Net Assets $ 505,300,892
Holdings Count | Holding 204
Investment Company Portfolio Turnover 51.00%
Additional Fund Statistics [Text Block]
KEY FUND STATISTICS (As of June 30, 2026)
Fund net assets $505,300,892
Total number of portfolio holdings 204
Portfolio turnover rate 51%
Holdings [Text Block]
WHAT DID THE FUND INVEST IN? (As of June 30, 2026)
The tables below show the investment makeup of the Fund, representing the percentage of total investments (excluding repurchase agreements held as collateral for securities lending arrangements) of the Fund.
Top Ten Holdings
Prysmian S.p.A. 1.2%
Glanbia PLC 1.1%
Deutsche Lufthansa AG 1.1%
HOCHTIEF AG 1.0%
Aberdeen Group PLC 1.0%
Acciona S.A. 1.0%
ACS Actividades de Construccion y Servicios S.A. 1.0%
JD Sports Fashion PLC 1.0%
Aurubis AG 1.0%
British Land (The) Co. PLC 0.9%
Sector Allocation
Graphical Representation - Allocation 2 Chart
Largest Holdings [Text Block]
Top Ten Holdings
Prysmian S.p.A. 1.2%
Glanbia PLC 1.1%
Deutsche Lufthansa AG 1.1%
HOCHTIEF AG 1.0%
Aberdeen Group PLC 1.0%
Acciona S.A. 1.0%
ACS Actividades de Construccion y Servicios S.A. 1.0%
JD Sports Fashion PLC 1.0%
Aurubis AG 1.0%
British Land (The) Co. PLC 0.9%
C000099051 [Member]  
Shareholder Report [Line Items]  
Fund Name First Trust Latin America AlphaDEX® Fund
Class Name First Trust Latin America AlphaDEX® Fund
Trading Symbol FLN
Security Exchange Name NASDAQ
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about the First Trust Latin America AlphaDEX® Fund (the “Fund”) for the period of January 1, 2026 to June 30, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the Fund at www.ftportfolios.com/fund-documents/etf/FLN. You can also request this information by contacting us at 1-800-621-1675 or info@ftportfolios.com.
Additional Information Phone Number 1-800-621-1675
Additional Information Email info@ftportfolios.com
Additional Information Website www.ftportfolios.com/fund-documents/etf/FLN
Expenses [Text Block]
WHAT WERE THE FUND COSTS FOR THE LAST SIX MONTHS?
(Based on a hypothetical $10,000 investment)
Fund Costs of a $10,000 investment Costs paid as a percentage
of a $10,000 investment
First Trust Latin America AlphaDEX® Fund $42 0.80%(1)
(1)
Annualized.
Expenses Paid, Amount $ 42
Expense Ratio, Percent 0.80% [3]
Net Assets $ 34,573,477
Holdings Count | Holding 51
Investment Company Portfolio Turnover 42.00%
Additional Fund Statistics [Text Block]
KEY FUND STATISTICS (As of June 30, 2026)
Fund net assets $34,573,477
Total number of portfolio holdings 51
Portfolio turnover rate 42%
Holdings [Text Block]
WHAT DID THE FUND INVEST IN? (As of June 30, 2026)
The tables below show the investment makeup of the Fund, representing the percentage of total investments of the Fund.
Top Ten Holdings
Eneva S.A. 3.8%
Coca-Cola Femsa S.A.B. de C.V. 3.8%
Fibra Uno Administracion S.A. de C.V. 3.7%
Cia Paranaense de Energia - Copel 3.4%
Vibra Energia S.A. 3.3%
Credicorp Ltd. 3.2%
Enel Chile S.A. 3.2%
Ultrapar Participacoes S.A. 3.2%
Cia Energetica de Minas Gerais 3.0%
Cemex S.A.B. de C.V., Series CPO 2.9%
Sector Allocation
Graphical Representation - Allocation 2 Chart
Any amount shown as 0.0% represents less than 0.1%.
Largest Holdings [Text Block]
Top Ten Holdings
Eneva S.A. 3.8%
Coca-Cola Femsa S.A.B. de C.V. 3.8%
Fibra Uno Administracion S.A. de C.V. 3.7%
Cia Paranaense de Energia - Copel 3.4%
Vibra Energia S.A. 3.3%
Credicorp Ltd. 3.2%
Enel Chile S.A. 3.2%
Ultrapar Participacoes S.A. 3.2%
Cia Energetica de Minas Gerais 3.0%
Cemex S.A.B. de C.V., Series CPO 2.9%
C000099053 [Member]  
Shareholder Report [Line Items]  
Fund Name First Trust China AlphaDEX® Fund
Class Name First Trust China AlphaDEX® Fund
Trading Symbol FCA
Security Exchange Name NASDAQ
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about the First Trust China AlphaDEX® Fund (the “Fund”) for the period of January 1, 2026 to June 30, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the Fund at www.ftportfolios.com/fund-documents/etf/FCA. You can also request this information by contacting us at 1-800-621-1675 or info@ftportfolios.com.
Additional Information Phone Number 1-800-621-1675
Additional Information Email info@ftportfolios.com
Additional Information Website www.ftportfolios.com/fund-documents/etf/FCA
Expenses [Text Block]
WHAT WERE THE FUND COSTS FOR THE LAST SIX MONTHS?
(Based on a hypothetical $10,000 investment)
Fund Costs of a $10,000 investment Costs paid as a percentage
of a $10,000 investment
First Trust China AlphaDEX® Fund $39 0.80%(1)
(1)
Annualized.
Expenses Paid, Amount $ 39
Expense Ratio, Percent 0.80% [4]
Net Assets $ 34,461,460
Holdings Count | Holding 51
Investment Company Portfolio Turnover 34.00%
Additional Fund Statistics [Text Block]
KEY FUND STATISTICS (As of June 30, 2026)
Fund net assets $34,461,460
Total number of portfolio holdings 51
Portfolio turnover rate 34%
Holdings [Text Block]
WHAT DID THE FUND INVEST IN? (As of June 30, 2026)
The tables below show the investment makeup of the Fund, representing the percentage of total investments (excluding repurchase agreements held as collateral for securities lending arrangements) of the Fund.
Top Ten Holdings
Yangtze Optical Fibre & Cable Joint Stock Ltd., Co., Class H 14.1%
Inner Mongolia Yitai Coal Co., Ltd., Class B 4.0%
JD Logistics, Inc. 3.7%
PetroChina Co., Ltd., Class H 3.6%
COSCO SHIPPING Holdings Co., Ltd., Class H 3.4%
Qingdao Port International Co., Ltd., Class H 3.2%
Dongfang Electric Corp., Ltd., Class H 3.0%
China National Building Material Co., Ltd., Class H 3.0%
China Coal Energy Co., Ltd., Class H 2.8%
China Life Insurance Co., Ltd., Class H 2.8%
Sector Allocation
Graphical Representation - Allocation 2 Chart
Largest Holdings [Text Block]
Top Ten Holdings
Yangtze Optical Fibre & Cable Joint Stock Ltd., Co., Class H 14.1%
Inner Mongolia Yitai Coal Co., Ltd., Class B 4.0%
JD Logistics, Inc. 3.7%
PetroChina Co., Ltd., Class H 3.6%
COSCO SHIPPING Holdings Co., Ltd., Class H 3.4%
Qingdao Port International Co., Ltd., Class H 3.2%
Dongfang Electric Corp., Ltd., Class H 3.0%
China National Building Material Co., Ltd., Class H 3.0%
China Coal Energy Co., Ltd., Class H 2.8%
China Life Insurance Co., Ltd., Class H 2.8%
C000099054 [Member]  
Shareholder Report [Line Items]  
Fund Name First Trust Japan AlphaDEX® Fund
Class Name First Trust Japan AlphaDEX® Fund
Trading Symbol FJP
Security Exchange Name NASDAQ
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about the First Trust Japan AlphaDEX® Fund (the “Fund”) for the period of January 1, 2026 to June 30, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the Fund at www.ftportfolios.com/fund-documents/etf/FJP. You can also request this information by contacting us at 1-800-621-1675 or info@ftportfolios.com.
Additional Information Phone Number 1-800-621-1675
Additional Information Email info@ftportfolios.com
Additional Information Website www.ftportfolios.com/fund-documents/etf/FJP
Expenses [Text Block]
WHAT WERE THE FUND COSTS FOR THE LAST SIX MONTHS?
(Based on a hypothetical $10,000 investment)
Fund Costs of a $10,000 investment Costs paid as a percentage
of a $10,000 investment
First Trust Japan AlphaDEX® Fund $42 0.80%(1)
(1)
Annualized.
Expenses Paid, Amount $ 42
Expense Ratio, Percent 0.80% [5]
Net Assets $ 253,827,254
Holdings Count | Holding 102
Investment Company Portfolio Turnover 34.00%
Additional Fund Statistics [Text Block]
KEY FUND STATISTICS (As of June 30, 2026)
Fund net assets $253,827,254
Total number of portfolio holdings 102
Portfolio turnover rate 34%
Holdings [Text Block]
WHAT DID THE FUND INVEST IN? (As of June 30, 2026)
The tables below show the investment makeup of the Fund, representing the percentage of total investments (excluding repurchase agreements held as collateral for securities lending arrangements) of the Fund.
Top Ten Holdings
Mitsui Kinzoku Co. 3.4%
NGK Insulators Ltd. 3.1%
Ibiden Co., Ltd. 3.0%
Fujikura Ltd. 2.4%
Resonac Holdings Corp. 2.3%
Sumitomo Electric Industries Ltd. 2.1%
Kandenko Co., Ltd. 1.9%
Advantest Corp. 1.9%
Kokusai Electric Corp. 1.7%
Tokyo Ohka Kogyo Co., Ltd. 1.6%
Sector Allocation
Graphical Representation - Allocation 2 Chart
Largest Holdings [Text Block]
Top Ten Holdings
Mitsui Kinzoku Co. 3.4%
NGK Insulators Ltd. 3.1%
Ibiden Co., Ltd. 3.0%
Fujikura Ltd. 2.4%
Resonac Holdings Corp. 2.3%
Sumitomo Electric Industries Ltd. 2.1%
Kandenko Co., Ltd. 1.9%
Advantest Corp. 1.9%
Kokusai Electric Corp. 1.7%
Tokyo Ohka Kogyo Co., Ltd. 1.6%
C000099056 [Member]  
Shareholder Report [Line Items]  
Fund Name First Trust Developed Markets ex-US AlphaDEX® Fund
Class Name First Trust Developed Markets ex-US AlphaDEX® Fund
Trading Symbol FDT
Security Exchange Name NASDAQ
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about the First Trust Developed Markets ex-US AlphaDEX® Fund (the “Fund”) for the period of January 1, 2026 to June 30, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the Fund at www.ftportfolios.com/fund-documents/etf/FDT. You can also request this information by contacting us at 1-800-621-1675 or info@ftportfolios.com.
Additional Information Phone Number 1-800-621-1675
Additional Information Email info@ftportfolios.com
Additional Information Website www.ftportfolios.com/fund-documents/etf/FDT
Expenses [Text Block]
WHAT WERE THE FUND COSTS FOR THE LAST SIX MONTHS?
(Based on a hypothetical $10,000 investment)
Fund Costs of a $10,000 investment Costs paid as a percentage
of a $10,000 investment
First Trust Developed Markets ex-US AlphaDEX® Fund $44 0.80%(1)
(1)
Annualized.
Expenses Paid, Amount $ 44
Expense Ratio, Percent 0.80% [6]
Net Assets $ 1,315,158,001
Holdings Count | Holding 303
Investment Company Portfolio Turnover 52.00%
Additional Fund Statistics [Text Block]
KEY FUND STATISTICS (As of June 30, 2026)
Fund net assets $1,315,158,001
Total number of portfolio holdings 303
Portfolio turnover rate 52%
Holdings [Text Block]
WHAT DID THE FUND INVEST IN? (As of June 30, 2026)
The tables below show the investment makeup of the Fund, representing the percentage of total investments (excluding repurchase agreements held as collateral for securities lending arrangements) of the Fund.
Top Ten Holdings
Samsung Electro-Mechanics Co., Ltd. 2.1%
Kingboard Laminates Holdings Ltd. 2.1%
Kingboard Holdings Ltd. 1.8%
SK Square Co., Ltd. 1.4%
LG Innotek Co., Ltd. 1.3%
SK hynix, Inc. 1.3%
SK, Inc. 0.8%
SoftBank Group Corp. 0.8%
Furukawa Electric Co., Ltd. 0.8%
Samsung Electronics Co., Ltd. 0.8%
Sector Allocation
Graphical Representation - Allocation 2 Chart
Largest Holdings [Text Block]
Top Ten Holdings
Samsung Electro-Mechanics Co., Ltd. 2.1%
Kingboard Laminates Holdings Ltd. 2.1%
Kingboard Holdings Ltd. 1.8%
SK Square Co., Ltd. 1.4%
LG Innotek Co., Ltd. 1.3%
SK hynix, Inc. 1.3%
SK, Inc. 0.8%
SoftBank Group Corp. 0.8%
Furukawa Electric Co., Ltd. 0.8%
Samsung Electronics Co., Ltd. 0.8%
C000099057 [Member]  
Shareholder Report [Line Items]  
Fund Name First Trust Asia Pacific ex-Japan AlphaDEX® Fund
Class Name First Trust Asia Pacific ex-Japan AlphaDEX® Fund
Trading Symbol FPA
Security Exchange Name NASDAQ
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about the First Trust Asia Pacific ex-Japan AlphaDEX® Fund (the “Fund”) for the period of January 1, 2026 to June 30, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the Fund at www.ftportfolios.com/fund-documents/etf/FPA. You can also request this information by contacting us at 1-800-621-1675 or info@ftportfolios.com.
Additional Information Phone Number 1-800-621-1675
Additional Information Email info@ftportfolios.com
Additional Information Website www.ftportfolios.com/fund-documents/etf/FPA
Expenses [Text Block]
WHAT WERE THE FUND COSTS FOR THE LAST SIX MONTHS?
(Based on a hypothetical $10,000 investment)
Fund Costs of a $10,000 investment Costs paid as a percentage
of a $10,000 investment
First Trust Asia Pacific ex-Japan AlphaDEX® Fund $48 0.80%(1)
(1)
Annualized.
Expenses Paid, Amount $ 48
Expense Ratio, Percent 0.80% [7]
Net Assets $ 123,824,391
Holdings Count | Holding 101
Investment Company Portfolio Turnover 71.00%
Additional Fund Statistics [Text Block]
KEY FUND STATISTICS (As of June 30, 2026)
Fund net assets $123,824,391
Total number of portfolio holdings 101
Portfolio turnover rate 71%
Holdings [Text Block]
WHAT DID THE FUND INVEST IN? (As of June 30, 2026)
The tables below show the investment makeup of the Fund, representing the percentage of total investments (excluding repurchase agreements held as collateral for securities lending arrangements) of the Fund.
Top Ten Holdings
Samsung Electro-Mechanics Co., Ltd. 6.9%
Kingboard Laminates Holdings Ltd. 5.4%
Kingboard Holdings Ltd. 4.7%
SK Square Co., Ltd. 3.7%
SK hynix, Inc. 3.4%
LG Innotek Co., Ltd. 2.6%
SK, Inc. 2.1%
Samsung Electronics Co., Ltd. 2.0%
Samsung Life Insurance Co., Ltd. 2.0%
Doosan Co., Ltd. 1.9%
Sector Allocation
Graphical Representation - Allocation 2 Chart
Largest Holdings [Text Block]
Top Ten Holdings
Samsung Electro-Mechanics Co., Ltd. 6.9%
Kingboard Laminates Holdings Ltd. 5.4%
Kingboard Holdings Ltd. 4.7%
SK Square Co., Ltd. 3.7%
SK hynix, Inc. 3.4%
LG Innotek Co., Ltd. 2.6%
SK, Inc. 2.1%
Samsung Electronics Co., Ltd. 2.0%
Samsung Life Insurance Co., Ltd. 2.0%
Doosan Co., Ltd. 1.9%
C000111808 [Member]  
Shareholder Report [Line Items]  
Fund Name First Trust Germany AlphaDEX® Fund
Class Name First Trust Germany AlphaDEX® Fund
Trading Symbol FGM
Security Exchange Name NASDAQ
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about the First Trust Germany AlphaDEX® Fund (the “Fund”) for the period of January 1, 2026 to June 30, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the Fund at www.ftportfolios.com/fund-documents/etf/FGM. You can also request this information by contacting us at 1-800-621-1675 or info@ftportfolios.com.
Additional Information Phone Number 1-800-621-1675
Additional Information Email info@ftportfolios.com
Additional Information Website www.ftportfolios.com/fund-documents/etf/FGM
Expenses [Text Block]
WHAT WERE THE FUND COSTS FOR THE LAST SIX MONTHS?
(Based on a hypothetical $10,000 investment)
Fund Costs of a $10,000 investment Costs paid as a percentage
of a $10,000 investment
First Trust Germany AlphaDEX® Fund $40 0.80%(1)
(1)
Annualized.
Expenses Paid, Amount $ 40
Expense Ratio, Percent 0.80% [8]
Net Assets $ 98,214,709
Holdings Count | Holding 41
Investment Company Portfolio Turnover 37.00%
Additional Fund Statistics [Text Block]
KEY FUND STATISTICS (As of June 30, 2026)
Fund net assets $98,214,709
Total number of portfolio holdings 41
Portfolio turnover rate 37%
Holdings [Text Block]
WHAT DID THE FUND INVEST IN? (As of June 30, 2026)
The tables below show the investment makeup of the Fund, representing the percentage of total investments (excluding repurchase agreements held as collateral for securities lending arrangements) of the Fund.
Top Ten Holdings
HOCHTIEF AG 6.1%
Aurubis AG 5.9%
Nordex SE 5.2%
Deutsche Lufthansa AG 4.8%
Bayer AG 4.2%
Schaeffler AG 4.1%
DHL Group 3.7%
thyssenkrupp AG 3.6%
LEG Immobilien SE 3.6%
Aroundtown S.A. 3.6%
Sector Allocation
Graphical Representation - Allocation 2 Chart
Largest Holdings [Text Block]
Top Ten Holdings
HOCHTIEF AG 6.1%
Aurubis AG 5.9%
Nordex SE 5.2%
Deutsche Lufthansa AG 4.8%
Bayer AG 4.2%
Schaeffler AG 4.1%
DHL Group 3.7%
thyssenkrupp AG 3.6%
LEG Immobilien SE 3.6%
Aroundtown S.A. 3.6%
C000111810 [Member]  
Shareholder Report [Line Items]  
Fund Name First Trust Switzerland AlphaDEX® Fund
Class Name First Trust Switzerland AlphaDEX® Fund
Trading Symbol FSZ
Security Exchange Name NASDAQ
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about the First Trust Switzerland AlphaDEX® Fund (the “Fund”) for the period of January 1, 2026 to June 30, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the Fund at www.ftportfolios.com/fund-documents/etf/FSZ. You can also request this information by contacting us at 1-800-621-1675 or info@ftportfolios.com.
Additional Information Phone Number 1-800-621-1675
Additional Information Email info@ftportfolios.com
Additional Information Website www.ftportfolios.com/fund-documents/etf/FSZ
Expenses [Text Block]
WHAT WERE THE FUND COSTS FOR THE LAST SIX MONTHS?
(Based on a hypothetical $10,000 investment)
Fund Costs of a $10,000 investment Costs paid as a percentage
of a $10,000 investment
First Trust Switzerland AlphaDEX® Fund $40 0.80%(1)
(1)
Annualized.
Expenses Paid, Amount $ 40
Expense Ratio, Percent 0.80% [9]
Net Assets $ 36,873,303
Holdings Count | Holding 41
Investment Company Portfolio Turnover 37.00%
Additional Fund Statistics [Text Block]
KEY FUND STATISTICS (As of June 30, 2026)
Fund net assets $36,873,303
Total number of portfolio holdings 41
Portfolio turnover rate 37%
Holdings [Text Block]
WHAT DID THE FUND INVEST IN? (As of June 30, 2026)
The tables below show the investment makeup of the Fund, representing the percentage of total investments of the Fund.
Top Ten Holdings
Sandoz Group AG 5.0%
SFS Group AG 4.9%
Galderma Group AG 4.5%
VAT Group AG 4.4%
SIG Group AG 3.8%
Holcim AG 3.7%
Avolta AG 3.7%
UBS Group AG 3.5%
Swisscom AG 3.5%
Bucher Industries AG 3.4%
Sector Allocation
Graphical Representation - Allocation 2 Chart
Largest Holdings [Text Block]
Top Ten Holdings
Sandoz Group AG 5.0%
SFS Group AG 4.9%
Galderma Group AG 4.5%
VAT Group AG 4.4%
SIG Group AG 3.8%
Holcim AG 3.7%
Avolta AG 3.7%
UBS Group AG 3.5%
Swisscom AG 3.5%
Bucher Industries AG 3.4%
C000111811 [Member]  
Shareholder Report [Line Items]  
Fund Name First Trust India NIFTY 50 Equal Weight ETF
Class Name First Trust India NIFTY 50 Equal Weight ETF
Trading Symbol NFTY
Security Exchange Name NASDAQ
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about the First Trust India NIFTY 50 Equal Weight ETF (the “Fund”) for the period of January 1, 2026 to June 30, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the Fund at www.ftportfolios.com/fund-documents/etf/NFTY. You can also request this information by contacting us at 1-800-621-1675 or info@ftportfolios.com.
Additional Information Phone Number 1-800-621-1675
Additional Information Email info@ftportfolios.com
Additional Information Website www.ftportfolios.com/fund-documents/etf/NFTY
Expenses [Text Block]
WHAT WERE THE FUND COSTS FOR THE LAST SIX MONTHS?
(Based on a hypothetical $10,000 investment)
Fund Costs of a $10,000 investment Costs paid as a percentage
of a $10,000 investment
First Trust India NIFTY 50 Equal Weight ETF $38 0.80%(1)
(1)
Annualized.
Expenses Paid, Amount $ 38
Expense Ratio, Percent 0.80% [10]
Net Assets $ 132,098,718
Holdings Count | Holding 50
Investment Company Portfolio Turnover 9.00%
Additional Fund Statistics [Text Block]
KEY FUND STATISTICS (As of June 30, 2026)
Fund net assets $132,098,718
Total number of portfolio holdings 50
Portfolio turnover rate 9%
Holdings [Text Block]
WHAT DID THE FUND INVEST IN? (As of June 30, 2026)
The tables below show the investment makeup of the Fund, representing the percentage of total investments of the Fund.
Top Ten Holdings
Maruti Suzuki India Ltd. 2.1%
Max Healthcare Institute Ltd. 2.1%
Eternal Ltd. 2.1%
InterGlobe Aviation Ltd. 2.1%
Shriram Finance Ltd. 2.1%
Dr. Reddy's Laboratories Ltd. 2.1%
Cipla Ltd. 2.0%
Titan Co., Ltd. 2.0%
Nestle India Ltd. 2.0%
Bajaj Finance Ltd. 2.0%
Sector Allocation
Graphical Representation - Allocation 2 Chart
Largest Holdings [Text Block]
Top Ten Holdings
Maruti Suzuki India Ltd. 2.1%
Max Healthcare Institute Ltd. 2.1%
Eternal Ltd. 2.1%
InterGlobe Aviation Ltd. 2.1%
Shriram Finance Ltd. 2.1%
Dr. Reddy's Laboratories Ltd. 2.1%
Cipla Ltd. 2.0%
Titan Co., Ltd. 2.0%
Nestle India Ltd. 2.0%
Bajaj Finance Ltd. 2.0%
C000111812 [Member]  
Shareholder Report [Line Items]  
Fund Name First Trust United Kingdom AlphaDEX® Fund
Class Name First Trust United Kingdom AlphaDEX® Fund
Trading Symbol FKU
Security Exchange Name NASDAQ
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about the First Trust United Kingdom AlphaDEX® Fund (the “Fund”) for the period of January 1, 2026 to June 30, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the Fund at www.ftportfolios.com/fund-documents/etf/FKU. You can also request this information by contacting us at 1-800-621-1675 or info@ftportfolios.com.
Additional Information Phone Number 1-800-621-1675
Additional Information Email info@ftportfolios.com
Additional Information Website www.ftportfolios.com/fund-documents/etf/FKU
Expenses [Text Block]
WHAT WERE THE FUND COSTS FOR THE LAST SIX MONTHS?
(Based on a hypothetical $10,000 investment)
Fund Costs of a $10,000 investment Costs paid as a percentage
of a $10,000 investment
First Trust United Kingdom AlphaDEX® Fund $41 0.80%(1)
(1)
Annualized.
Expenses Paid, Amount $ 41
Expense Ratio, Percent 0.80% [11]
Net Assets $ 36,723,685
Holdings Count | Holding 76
Investment Company Portfolio Turnover 40.00%
Additional Fund Statistics [Text Block]
KEY FUND STATISTICS (As of June 30, 2026)
Fund net assets $36,723,685
Total number of portfolio holdings 76
Portfolio turnover rate 40%
Holdings [Text Block]
WHAT DID THE FUND INVEST IN? (As of June 30, 2026)
The tables below show the investment makeup of the Fund, representing the percentage of total investments of the Fund.
Top Ten Holdings
Beazley PLC 3.3%
Balfour Beatty PLC 2.6%
Lion Finance Group PLC 2.6%
Standard Chartered PLC 2.4%
IG Group Holdings PLC 2.4%
easyJet PLC 2.3%
Shell PLC 2.3%
Barclays PLC 2.3%
Tritax Big Box REIT PLC 2.3%
Glencore PLC 2.2%
Sector Allocation
Graphical Representation - Allocation 2 Chart
Largest Holdings [Text Block]
Top Ten Holdings
Beazley PLC 3.3%
Balfour Beatty PLC 2.6%
Lion Finance Group PLC 2.6%
Standard Chartered PLC 2.4%
IG Group Holdings PLC 2.4%
easyJet PLC 2.3%
Shell PLC 2.3%
Barclays PLC 2.3%
Tritax Big Box REIT PLC 2.3%
Glencore PLC 2.2%
C000112036 [Member]  
Shareholder Report [Line Items]  
Fund Name First Trust Developed Markets ex-US Small Cap AlphaDEX® Fund
Class Name First Trust Developed Markets ex-US Small Cap AlphaDEX® Fund
Trading Symbol FDTS
Security Exchange Name NASDAQ
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about the First Trust Developed Markets ex-US Small Cap AlphaDEX® Fund (the “Fund”) for the period of January 1, 2026 to June 30, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the Fund at www.ftportfolios.com/fund-documents/etf/FDTS. You can also request this information by contacting us at 1-800-621-1675 or info@ftportfolios.com.
Additional Information Phone Number 1-800-621-1675
Additional Information Email info@ftportfolios.com
Additional Information Website www.ftportfolios.com/fund-documents/etf/FDTS
Expenses [Text Block]
WHAT WERE THE FUND COSTS FOR THE LAST SIX MONTHS?
(Based on a hypothetical $10,000 investment)
Fund Costs of a $10,000 investment Costs paid as a percentage
of a $10,000 investment
First Trust Developed Markets ex-US Small Cap AlphaDEX® Fund $42 0.80%(1)
(1)
Annualized.
Expenses Paid, Amount $ 42
Expense Ratio, Percent 0.80% [12]
Net Assets $ 13,047,785
Holdings Count | Holding 407
Investment Company Portfolio Turnover 70.00%
Additional Fund Statistics [Text Block]
KEY FUND STATISTICS (As of June 30, 2026)
Fund net assets $13,047,785
Total number of portfolio holdings 407
Portfolio turnover rate 70%
Holdings [Text Block]
WHAT DID THE FUND INVEST IN? (As of June 30, 2026)
The tables below show the investment makeup of the Fund, representing the percentage of total investments (excluding repurchase agreements held as collateral for securities lending arrangements) of the Fund.
Top Ten Holdings
Shinsegae, Inc. 1.0%
Jeju Semiconductor Corp. 0.9%
GigaVis Co., Ltd. 0.8%
PSK, Inc. 0.8%
TSE Co., Ltd. 0.7%
Daeduck Electronics Co., Ltd. 0.6%
TES Co., Ltd. 0.6%
Tsugami Corp. 0.6%
Fuji Corp. 0.6%
Korea Circuit Co., Ltd. 0.5%
Sector Allocation
Graphical Representation - Allocation 2 Chart
Largest Holdings [Text Block]
Top Ten Holdings
Shinsegae, Inc. 1.0%
Jeju Semiconductor Corp. 0.9%
GigaVis Co., Ltd. 0.8%
PSK, Inc. 0.8%
TSE Co., Ltd. 0.7%
Daeduck Electronics Co., Ltd. 0.6%
TES Co., Ltd. 0.6%
Tsugami Corp. 0.6%
Fuji Corp. 0.6%
Korea Circuit Co., Ltd. 0.5%
C000112037 [Member]  
Shareholder Report [Line Items]  
Fund Name First Trust Emerging Markets Small Cap AlphaDEX® Fund
Class Name First Trust Emerging Markets Small Cap AlphaDEX® Fund
Trading Symbol FEMS
Security Exchange Name NASDAQ
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about the First Trust Emerging Markets Small Cap AlphaDEX® Fund (the “Fund”) for the period of January 1, 2026 to June 30, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the Fund at www.ftportfolios.com/fund-documents/etf/FEMS. You can also request this information by contacting us at 1-800-621-1675 or info@ftportfolios.com.
Additional Information Phone Number 1-800-621-1675
Additional Information Email info@ftportfolios.com
Additional Information Website www.ftportfolios.com/fund-documents/etf/FEMS
Expenses [Text Block]
WHAT WERE THE FUND COSTS FOR THE LAST SIX MONTHS?
(Based on a hypothetical $10,000 investment)
Fund Costs of a $10,000 investment Costs paid as a percentage
of a $10,000 investment
First Trust Emerging Markets Small Cap AlphaDEX® Fund $41 0.80%(1)
(1)
Annualized.
Expenses Paid, Amount $ 41
Expense Ratio, Percent 0.80% [13]
Net Assets $ 251,797,729
Holdings Count | Holding 206
Investment Company Portfolio Turnover 69.00%
Additional Fund Statistics [Text Block]
KEY FUND STATISTICS (As of June 30, 2026)
Fund net assets $251,797,729
Total number of portfolio holdings 206
Portfolio turnover rate 69%
Holdings [Text Block]
WHAT DID THE FUND INVEST IN? (As of June 30, 2026)
The tables below show the investment makeup of the Fund, representing the percentage of total investments (excluding repurchase agreements held as collateral for securities lending arrangements) of the Fund.
Top Ten Holdings
ITEQ Corp. 2.0%
Holy Stone Enterprise Co., Ltd. 2.0%
Katilimevim Tasarruf Finansman A/S 1.7%
Europower Enerji VE Otomasyon Teknolojileri Sanayi Ticaret A/S 1.6%
Topoint Technology Co., Ltd. 1.5%
Kaori Heat Treatment Co., Ltd. 1.5%
ChipMOS Technologies, Inc. 1.2%
AmTRAN Technology Co., Ltd. 1.1%
Thaifoods Group PCL 1.0%
Pell Bio-Med Technology Co., Ltd. 1.0%
Sector Allocation
Graphical Representation - Allocation 2 Chart
Largest Holdings [Text Block]
Top Ten Holdings
ITEQ Corp. 2.0%
Holy Stone Enterprise Co., Ltd. 2.0%
Katilimevim Tasarruf Finansman A/S 1.7%
Europower Enerji VE Otomasyon Teknolojileri Sanayi Ticaret A/S 1.6%
Topoint Technology Co., Ltd. 1.5%
Kaori Heat Treatment Co., Ltd. 1.5%
ChipMOS Technologies, Inc. 1.2%
AmTRAN Technology Co., Ltd. 1.1%
Thaifoods Group PCL 1.0%
Pell Bio-Med Technology Co., Ltd. 1.0%
C000147004 [Member]  
Shareholder Report [Line Items]  
Fund Name First Trust Eurozone AlphaDEX® ETF
Class Name First Trust Eurozone AlphaDEX® ETF
Trading Symbol FEUZ
Security Exchange Name NASDAQ
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about the First Trust Eurozone AlphaDEX® ETF (the “Fund”) for the period of January 1, 2026 to June 30, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the Fund at www.ftportfolios.com/fund-documents/etf/FEUZ. You can also request this information by contacting us at 1-800-621-1675 or info@ftportfolios.com.
Additional Information Phone Number 1-800-621-1675
Additional Information Email info@ftportfolios.com
Additional Information Website www.ftportfolios.com/fund-documents/etf/FEUZ
Expenses [Text Block]
WHAT WERE THE FUND COSTS FOR THE LAST SIX MONTHS?
(Based on a hypothetical $10,000 investment)
Fund Costs of a $10,000 investment Costs paid as a percentage
of a $10,000 investment
First Trust Eurozone AlphaDEX® ETF $42 0.80%(1)
(1)
Annualized.
Expenses Paid, Amount $ 42
Expense Ratio, Percent 0.80% [14]
Net Assets $ 136,063,647
Holdings Count | Holding 153
Investment Company Portfolio Turnover 46.00%
Additional Fund Statistics [Text Block]
KEY FUND STATISTICS (As of June 30, 2026)
Fund net assets $136,063,647
Total number of portfolio holdings 153
Portfolio turnover rate 46%
Holdings [Text Block]
WHAT DID THE FUND INVEST IN? (As of June 30, 2026)
The tables below show the investment makeup of the Fund, representing the percentage of total investments (excluding repurchase agreements held as collateral for securities lending arrangements) of the Fund.
Top Ten Holdings
Prysmian S.p.A. 1.5%
Glanbia PLC 1.5%
Deutsche Lufthansa AG 1.4%
HOCHTIEF AG 1.4%
Acciona S.A. 1.3%
ASML Holding N.V. 1.3%
ACS Actividades de Construccion y Servicios S.A. 1.3%
Aurubis AG 1.2%
ArcelorMittal S.A. 1.2%
Schaeffler AG 1.2%
Sector Allocation
Graphical Representation - Allocation 2 Chart
Largest Holdings [Text Block]
Top Ten Holdings
Prysmian S.p.A. 1.5%
Glanbia PLC 1.5%
Deutsche Lufthansa AG 1.4%
HOCHTIEF AG 1.4%
Acciona S.A. 1.3%
ASML Holding N.V. 1.3%
ACS Actividades de Construccion y Servicios S.A. 1.3%
Aurubis AG 1.2%
ArcelorMittal S.A. 1.2%
Schaeffler AG 1.2%
[1] Annualized.
[2] Annualized.
[3]
Annualized.
[4]
Annualized.
[5]
Annualized.
[6]
Annualized.
[7] Annualized.
[8] Annualized.
[9]
Annualized.
[10]
Annualized.
[11]
Annualized.
[12]
Annualized.
[13]
Annualized.
[14]
Annualized.