v3.25.4
First Trust Short Duration High Income Fund Average Annual Total Returns
 12 Months Ended 60 Months Ended 120 Months Ended 158 Months Ended
Oct. 31, 2025
Dec. 31, 2025
Dec. 31, 2025
Dec. 31, 2025
Dec. 31, 2025
FDHAX Blended Index (reflects no deduction for fees, expenses or taxes)[Member]          
Prospectus [Line Items]          
Average Annual Return, Percent [1],[2]   7.20% 5.49% 6.16% 5.22%
Performance Inception Date [1],[2] Nov. 01, 2012        
ICE BofA US High Yield Constrained Index (reflects no deduction for fees, expenses or taxes)[Member]          
Prospectus [Line Items]          
Average Annual Return, Percent [1]   8.50% 4.50% 6.44% 5.42%
Performance Inception Date [1] Nov. 01, 2012        
Morningstar® LSTA® US Leveraged Loan Index (reflects no deduction for fees, expenses or taxes)[Member]          
Prospectus [Line Items]          
Average Annual Return, Percent [1]   5.90% 6.42% 5.83% 4.96%
Performance Inception Date [1] Nov. 01, 2012        
Bloomberg U.S. Aggregate Bond Index (reflects no deduction for fees, expenses or taxes)[Member]          
Prospectus [Line Items]          
Average Annual Return, Percent [1]   7.30% (0.36%) 2.01% 1.86%
Performance Inception Date [1] Nov. 01, 2012        
C | Return Before Taxes[Member]          
Prospectus [Line Items]          
Average Annual Return, Percent   5.22% 3.57% 3.85% 3.41%
Performance Inception Date Nov. 01, 2012        
I | Return Before Taxes[Member]          
Prospectus [Line Items]          
Average Annual Return, Percent   7.28% 4.60% 4.89% 4.44%
Performance Inception Date Nov. 01, 2012        
A | After Taxes on Distributions          
Prospectus [Line Items]          
Average Annual Return, Percent   0.74% 1.20% 2.10% 1.84%
Performance Inception Date Nov. 01, 2012        
A | After Taxes on Distributions and Sales          
Prospectus [Line Items]          
Average Annual Return, Percent   1.89% 1.68% 2.29% 2.04%
Performance Inception Date Nov. 01, 2012        
A | Return Before Taxes[Member]          
Prospectus [Line Items]          
Average Annual Return, Percent   3.29% 3.60% 4.25% 3.90%
Performance Inception Date Nov. 01, 2012        
[1] Since inception return is based on the Class I Shares inception date.
[2] The Blended Index return is a 50/50 split between the ICE BofA US High Yield Constrained Index and the Morningstar® LSTA® US Leveraged Loan Index returns.