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First Trust Consumer Discretionary AlphaDEX Fund Average Annual Total Returns
 12 Months Ended 60 Months Ended 120 Months Ended 164 Months Ended 212 Months Ended
Jul. 31, 2025
Dec. 31, 2024
Dec. 31, 2024
Dec. 31, 2024
Dec. 31, 2024
Dec. 31, 2024
StrataQuant® Consumer Discretionary Index (reflects no deduction for fees, expenses or taxes)[Member]            
Prospectus [Line Items]            
Average Annual Return, Percent   11.27% 8.85% 7.71%   8.46%
Russell 1000® Index (reflects no deduction for fees, expenses or taxes)[Member]            
Prospectus [Line Items]            
Average Annual Return, Percent   24.51% 14.28% 12.87%   10.12%
S&P 500® Consumer Discretionary Index (reflects no deduction for fees, expenses or taxes)[Member]            
Prospectus [Line Items]            
Average Annual Return, Percent   30.14% 14.12% 13.62%   12.08%
Russell 1000® Consumer Discretionary Index (reflects no deduction for fees, expenses or taxes)[Member]            
Prospectus [Line Items]            
Average Annual Return, Percent [1]   30.31% 14.30% 13.45%  
Russell 3000® Index (reflects no deduction for fees, expenses or taxes)[Member]            
Prospectus [Line Items]            
Average Annual Return, Percent   23.81% 13.86% 12.55% 13.21% 9.93%
First Trust Consumer Discretionary AlphaDEX Fund            
Prospectus [Line Items]            
Average Annual Return, Percent   10.73% 8.22% 7.05%   7.73%
Performance Inception Date May 08, 2007          
First Trust Consumer Discretionary AlphaDEX Fund | After Taxes on Distributions            
Prospectus [Line Items]            
Average Annual Return, Percent   10.32% 7.87% 6.66%   7.39%
First Trust Consumer Discretionary AlphaDEX Fund | After Taxes on Distributions and Sales            
Prospectus [Line Items]            
Average Annual Return, Percent   6.35% 6.30% 5.48%   6.34%
[1] Performance data is not available for all the periods shown in the table for the index because performance data does not exist for some of the entire periods.