v3.26.1
First Trust S and P REIT Index Fund Average Annual Total Returns
 12 Months Ended 60 Months Ended 120 Months Ended 198 Months Ended 224 Months Ended 227 Months Ended 237 Months Ended 243 Months Ended
Dec. 31, 2025
Dec. 31, 2025
Dec. 31, 2025
Dec. 31, 2025
Dec. 31, 2025
Dec. 31, 2025
Dec. 31, 2025
Dec. 31, 2025
Dec. 31, 2025
S&P United States REIT Index (reflects no deduction for fees, expenses or taxes)[Member]                  
Prospectus [Line Items]                  
Average Annual Return, Percent [1]   3.01% 6.58% 5.59%        
FTSE EPRA/NAREIT North America Index (reflects no deduction for fees, expenses or taxes)[Member]                  
Prospectus [Line Items]                  
Average Annual Return, Percent   3.17% 6.06% 5.07%   4.55%      
Russell 3000® Index (reflects no deduction for fees, expenses or taxes)[Member]                  
Prospectus [Line Items]                  
Average Annual Return, Percent   17.15% 13.15% 14.29% 14.72% 10.31% 10.40% 10.67% 10.80%
First Trust S and P REIT Index Fund                  
Prospectus [Line Items]                  
Average Annual Return, Percent   2.82% 6.16% 5.10%   4.49%      
Performance Inception Date May 08, 2007                
First Trust S and P REIT Index Fund | After Taxes on Distributions                  
Prospectus [Line Items]                  
Average Annual Return, Percent   1.58% 4.99% 3.88%   3.36%      
First Trust S and P REIT Index Fund | After Taxes on Distributions and Sales                  
Prospectus [Line Items]                  
Average Annual Return, Percent   1.66% 4.28% 3.43%   3.02%      
[1] On November 6, 2008, the Fund’s underlying index changed from the S&P REIT Composite Index to the S&P United States REIT Index. Effective December 31, 2008, the S&P REIT Composite Index was discontinued. Therefore, the Fund’s performance and historical returns shown for the periods prior to November 6, 2008, are not necessarily indicative of the performance that the Fund, based on its current Index, would have generated. The inception date of the Index was June 30, 2008. Returns for the Index are only disclosed for those periods in which the Index was in existence for the whole period.