v3.26.1
First Trust Germany AlphaDEX Fund Average Annual Total Returns
 12 Months Ended 60 Months Ended 120 Months Ended 167 Months Ended
Dec. 31, 2025
Dec. 31, 2025
Dec. 31, 2025
Dec. 31, 2025
Dec. 31, 2025
Nasdaq AlphaDEX® Germany™ Index (reflects no deduction for fees, expenses or taxes)[Member]          
Prospectus [Line Items]          
Average Annual Return, Percent [1]   64.56% 6.78% 8.20%
Nasdaq Germany™ Index (reflects no deduction for fees, expenses or taxes)[Member]          
Prospectus [Line Items]          
Average Annual Return, Percent [1]   36.25% 8.05% 7.15%
MSCI Germany Index (reflects no deduction for fees, expenses or taxes)[Member]          
Prospectus [Line Items]          
Average Annual Return, Percent   36.28% 8.61% 7.59% 7.49%
First Trust Germany AlphaDEX Fund          
Prospectus [Line Items]          
Average Annual Return, Percent   63.48% 6.61% 7.94% 7.61%
Performance Inception Date Feb. 14, 2012        
First Trust Germany AlphaDEX Fund | After Taxes on Distributions          
Prospectus [Line Items]          
Average Annual Return, Percent   63.04% 5.50% 6.95% 6.71%
First Trust Germany AlphaDEX Fund | After Taxes on Distributions and Sales          
Prospectus [Line Items]          
Average Annual Return, Percent   37.58% 4.53% 5.86% 5.75%
[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.