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First Trust Emerging Markets Small Cap 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 Small Cap™ Index (reflects no deduction for fees, expenses or taxes)[Member]            
Prospectus [Line Items]            
Average Annual Return, Percent [1]   16.99% 7.16% 10.72%  
Nasdaq Emerging Markets Small Cap™ Index (reflects no deduction for fees, expenses or taxes)[Member]            
Prospectus [Line Items]            
Average Annual Return, Percent [1]   15.24% 6.08% 8.12%  
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 Small Cap AlphaDEX Fund            
Prospectus [Line Items]            
Average Annual Return, Percent   15.61% 5.54% 8.98% 6.43%  
Performance Inception Date Feb. 15, 2012          
First Trust Emerging Markets Small Cap AlphaDEX Fund | After Taxes on Distributions            
Prospectus [Line Items]            
Average Annual Return, Percent   13.63% 3.52% 7.12% 4.80%  
First Trust Emerging Markets Small Cap AlphaDEX Fund | After Taxes on Distributions and Sales            
Prospectus [Line Items]            
Average Annual Return, Percent   9.21% 3.33% 6.32% 4.34%  
[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.