v3.25.2
Average Annual Total Returns
 12 Months Ended 60 Months Ended 120 Months Ended
Dec. 31, 2024
Dec. 31, 2024
Dec. 31, 2024
S&P Municipal Bond Index (reflects no deduction for fees, expenses or taxes)[Member]      
Prospectus [Line Items]      
Average Annual Return, Percent [1] 1.90% 1.19% 2.34%
S&P Municipal Bond Intermediate Index(reflects no deduction for fees, expenses or taxes)[Member]      
Prospectus [Line Items]      
Average Annual Return, Percent [2] 1.09% 1.11% 2.20%
Morningstar Municipal National Intermediate Funds Average[Member]      
Prospectus [Line Items]      
Average Annual Return, Percent [3] 1.83% 0.92% 1.88%
A      
Prospectus [Line Items]      
Average Annual Return, Percent [4] (3.19%) 0.09% 1.52%
A | After Taxes on Distributions      
Prospectus [Line Items]      
Average Annual Return, Percent [4] (3.19%) 0.04% 1.42%
A | After Taxes on Distributions and Sales      
Prospectus [Line Items]      
Average Annual Return, Percent [4] (0.76%) 0.55% 1.63%
IS      
Prospectus [Line Items]      
Average Annual Return, Percent [4] 1.58% 1.28% 2.22%
[1] The S&P Municipal Bond Index is a broad, market value-weighted index that seeks to measure the performance of the U.S. municipal bond market. It tracks fixed-rate tax-free bonds and bonds subject to the alternative minimum tax (AMT). The index includes bonds of all quality–from AAA to non-rated, including defaulted bonds–from all sectors of the municipal bond market.
[2] The S&P Municipal Bond Intermediate Index consists of bonds in the S&P Municipal Bond Index with a minimum maturity of 3 years and a maximum maturity of 15 years. The S&P Municipal Bond Index is designed to track fixed-rate tax-free bonds and bonds subject to the alternative minimum tax (AMT). The S&P Municipal Bond Index includes bonds of all quality–from AAA to non-rated, including defaulted bonds–and from all sectors of the municipal bond market.
[3] Morningstar figures represent the average of the total returns reported by all the mutual funds designated by Morningstar as falling into the respective category indicated.
[4] Prior to December 29, 2017, Institutional Shares (IS) were designated as Class Y Shares and Service Shares (SS) were designated as Institutional Shares.