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First Trust SMID Growth Strength ETF Average Annual Total Returns
12 Months Ended 60 Months Ended 90 Months Ended
Mar. 31, 2025
Dec. 31, 2024
Dec. 31, 2024
Dec. 31, 2024
The SMID Growth Strength Index (reflects no deduction for fees, expenses or taxes)[Member]        
Prospectus [Line Items]        
Average Annual Return, Percent [1],[2]  
Nasdaq Riskalyze US Small Cap(TM) Index (reflects no deduction for fees, expenses or taxes)[Member]        
Prospectus [Line Items]        
Average Annual Return, Percent   7.69% 9.07% 8.50%
Russell 3000® Index (reflects no deduction for fees, expenses or taxes)[Member]        
Prospectus [Line Items]        
Average Annual Return, Percent   23.81% 13.86% 13.72%
S&P 1000® Index (reflects no deduction for fees, expenses or taxes)[Member]        
Prospectus [Line Items]        
Average Annual Return, Percent   12.34% 9.75% 9.43%
First Trust SMID Growth Strength ETF        
Prospectus [Line Items]        
Average Annual Return, Percent   6.45% 8.25% 7.71%
Performance Inception Date Jun. 20, 2017      
First Trust SMID Growth Strength ETF | After Taxes on Distributions        
Prospectus [Line Items]        
Average Annual Return, Percent   5.26% 7.36% 6.83%
First Trust SMID Growth Strength ETF | After Taxes on Distributions and Sales        
Prospectus [Line Items]        
Average Annual Return, Percent   3.79% 6.07% 5.71%
[1] On December 3, 2024, the Fund’s underlying index changed from the Nasdaq Riskalyze US Small CapTM Index to The SMID Growth Strength Index. Therefore, any Fund performance and historical returns shown above that incorporate Fund performance prior to December 3, 2024 reflect performance of the Fund based on the Nasdaq Riskalyze US Small CapTM Index and are not necessarily indicative of the performance that the Fund, based on The SMID Growth Strength Index, would have generated.
[2] 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.