v3.25.2
Shareholder Report, Line Graph (Details) - USD ($)
 12 Months Ended 24 Months Ended 36 Months Ended 48 Months Ended 60 Months Ended 72 Months Ended 84 Months Ended 96 Months Ended 108 Months Ended 120 Months Ended
May 31, 2015
May 31, 2025
May 31, 2016
May 31, 2017
May 31, 2018
May 31, 2019
May 31, 2020
May 31, 2021
May 31, 2022
May 31, 2023
May 31, 2024
May 31, 2025
C000015145 [Member]                        
Account Value [Line Items]                        
Line Graph and Table Measure Name   Class A Shares at maximum sales charge (Offering Price)                    
Accumulated Value $ 9,699   $ 10,139 $ 10,201 $ 10,188 $ 10,731 $ 11,168 $ 11,469 $ 10,701 $ 10,730 $ 10,993 $ 11,231
C000015146 [Member]                        
Account Value [Line Items]                        
Line Graph and Table Measure Name   Class I Shares at NAV                    
Accumulated Value 10,000   10,482 10,564 10,579 11,162 11,636 11,972 11,198 11,250 11,547 11,821
C000015139 [Member]                        
Account Value [Line Items]                        
Line Graph and Table Measure Name   Class A Shares at maximum sales charge (Offering Price)                    
Accumulated Value 9,582   10,165 10,197 10,297 10,805 11,292 11,634 10,664 10,536 10,719 10,776
C000015141 [Member]                        
Account Value [Line Items]                        
Line Graph and Table Measure Name   Class I Shares at NAV                    
Accumulated Value 10,000   10,625 10,677 10,799 11,362 11,897 12,283 11,286 11,174 11,392 11,462
C000015138 [Member]                        
Account Value [Line Items]                        
Line Graph and Table Measure Name   Class I Shares at NAV                    
Accumulated Value 10,000   10,661 10,781 10,982 11,623 11,927 12,551 11,717 11,645 12,028 12,221
C000015136 [Member]                        
Account Value [Line Items]                        
Line Graph and Table Measure Name   Class A Shares at maximum sales charge (Offering Price)                    
Accumulated Value 9,582   10,202 10,296 10,466 11,054 11,319 11,887 11,076 10,995 11,324 11,484
C000015134 [Member]                        
Account Value [Line Items]                        
Line Graph and Table Measure Name   Class A Shares at maximum sales charge (Offering Price)                    
Accumulated Value 9,702   10,202 10,292 10,386 10,921 11,202 11,617 10,948 11,026 11,276 11,562
C000015135 [Member]                        
Account Value [Line Items]                        
Line Graph and Table Measure Name   Class I Shares at NAV                    
Accumulated Value 10,000   10,536 10,647 10,764 11,352 11,665 12,120 11,451 11,554 11,839 12,163
S And P Municipal Bond Index [Member]                        
Account Value [Line Items]                        
Line Graph and Table Measure Name   S&P Municipal Bond Index                    
Accumulated Value 10,000   10,571 10,738 10,873 11,532 11,979 12,542 11,793 11,815 12,155 12,452
Lipper Other States Intermediate Municipal Debt Funds Classification Average [Member]                        
Account Value [Line Items]                        
Line Graph and Table Measure Name   Lipper Other States Intermediate Municipal Debt Funds Classification Average                    
S And P Municipal Bond Intermediate Index [Member]                        
Account Value [Line Items]                        
Line Graph and Table Measure Name   S&P Municipal Bond Intermediate Index                    
Accumulated Value 10,000   10,540 10,721 10,762 11,450 11,942 12,385 11,655 11,777 12,011 12,429
Lipper Other States Municipal Debt Funds Classification Average [Member]                        
Account Value [Line Items]                        
Line Graph and Table Measure Name   Lipper Other States Municipal Debt Funds Classification Average                    
S And P Municipal Bond Nebraska Index [Member]                        
Account Value [Line Items]                        
Line Graph and Table Measure Name   S&P Municipal Bond Nebraska Index                    
Accumulated Value 10,000   10,594 10,738 10,864 11,489 12,085 12,462 11,673 11,675 11,956 12,261
S And P Municipal Bond Minnesota Index [Member]                        
Account Value [Line Items]                        
Line Graph and Table Measure Name   S&P Municipal Bond Minnesota Index                    
Accumulated Value $ 10,000   $ 10,477 $ 10,633 $ 10,722 $ 11,349 $ 11,800 $ 12,252 $ 11,608 $ 11,580 $ 11,823 $ 12,179
Lipper Minnesota Municipal Debt Funds Classification Average [Member]                        
Account Value [Line Items]                        
Line Graph and Table Measure Name   Lipper Minnesota Municipal Debt Funds Classification Average