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First Trust Asia Pacific ex-Japan AlphaDEX Fund Average Annual Total Returns
 12 Months Ended 60 Months Ended 120 Months Ended 176 Months Ended
Dec. 31, 2025
Dec. 31, 2025
Dec. 31, 2025
Dec. 31, 2025
Dec. 31, 2025
Nasdaq AlphaDEX® Asia Pacific Ex-Japan™ Index (reflects no deduction for fees, expenses or taxes)[Member]          
Prospectus [Line Items]          
Average Annual Return, Percent [1]   43.92% 8.57% 7.68%
Nasdaq Developed Markets Asia Pacific Ex-Japan™ Index (reflects no deduction for fees, expenses or taxes)[Member]          
Prospectus [Line Items]          
Average Annual Return, Percent [1]   40.29% 5.76% 8.08%
MSCI Pacific ex-Japan Index (reflects no deduction for fees, expenses or taxes)[Member]          
Prospectus [Line Items]          
Average Annual Return, Percent   20.62% 5.74% 7.34% 4.90%
First Trust Asia Pacific ex-Japan AlphaDEX Fund          
Prospectus [Line Items]          
Average Annual Return, Percent   42.31% 7.23% 6.57% 4.75%
Performance Inception Date Apr. 18, 2011        
First Trust Asia Pacific ex-Japan AlphaDEX Fund | After Taxes on Distributions          
Prospectus [Line Items]          
Average Annual Return, Percent   39.51% 5.49% 5.11% 3.43%
First Trust Asia Pacific ex-Japan AlphaDEX Fund | After Taxes on Distributions and Sales          
Prospectus [Line Items]          
Average Annual Return, Percent   24.95% 4.76% 4.47% 3.08%
[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.