v3.26.1
First Trust Switzerland 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® Switzerland™ Index (reflects no deduction for fees, expenses or taxes)[Member]          
Prospectus [Line Items]          
Average Annual Return, Percent [1]   30.86% 8.57% 9.89%
Nasdaq Switzerland™ Index (reflects no deduction for fees, expenses or taxes)[Member]          
Prospectus [Line Items]          
Average Annual Return, Percent [1]   33.36% 8.02% 8.57%
MSCI Switzerland Index (reflects no deduction for fees, expenses or taxes)[Member]          
Prospectus [Line Items]          
Average Annual Return, Percent   33.47% 8.08% 8.73% 9.07%
First Trust Switzerland AlphaDEX Fund          
Prospectus [Line Items]          
Average Annual Return, Percent   30.16% 8.18% 9.51% 9.54%
Performance Inception Date Feb. 14, 2012        
First Trust Switzerland AlphaDEX Fund | After Taxes on Distributions          
Prospectus [Line Items]          
Average Annual Return, Percent   29.18% 7.19% 8.58% 8.64%
First Trust Switzerland AlphaDEX Fund | After Taxes on Distributions and Sales          
Prospectus [Line Items]          
Average Annual Return, Percent   17.83% 5.92% 7.26% 7.46%
[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.