v3.26.1
First Trust Emerging Markets AlphaDEX Fund Average Annual Total Returns
 12 Months Ended 60 Months Ended 120 Months Ended 167 Months Ended 176 Months Ended
Dec. 31, 2025
Dec. 31, 2025
Dec. 31, 2025
Dec. 31, 2025
Dec. 31, 2025
Dec. 31, 2025
Nasdaq AlphaDEX® Emerging Markets™ Index (reflects no deduction for fees, expenses or taxes)[Member]            
Prospectus [Line Items]            
Average Annual Return, Percent [1]   27.73% 7.26% 9.33%  
Nasdaq Emerging Markets™ Index (reflects no deduction for fees, expenses or taxes)[Member]            
Prospectus [Line Items]            
Average Annual Return, Percent [1]   27.14% 6.03% 8.89%  
MSCI Emerging Markets Index (reflects no deduction for fees, expenses or taxes)[Member]            
Prospectus [Line Items]            
Average Annual Return, Percent   33.57% 4.20% 8.42% 4.57% 3.79%
First Trust Emerging Markets AlphaDEX Fund            
Prospectus [Line Items]            
Average Annual Return, Percent   26.35% 6.13% 8.12%   2.94%
Performance Inception Date Apr. 18, 2011          
First Trust Emerging Markets AlphaDEX Fund | After Taxes on Distributions            
Prospectus [Line Items]            
Average Annual Return, Percent   24.67% 4.24% 6.49%   1.55%
First Trust Emerging Markets AlphaDEX Fund | After Taxes on Distributions and Sales            
Prospectus [Line Items]            
Average Annual Return, Percent   15.53% 3.81% 5.70%   1.57%
[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.