v3.25.2
Shareholder Report, Line Graph (Details) - USD ($)
 2 Months Ended 12 Months Ended
Apr. 10, 2017
Jun. 01, 2015
May 31, 2017
May 31, 2025
May 31, 2024
May 31, 2023
May 31, 2022
May 31, 2021
May 31, 2020
May 31, 2019
May 31, 2018
May 31, 2017
May 31, 2016
C000017685 [Member]                          
Account Value [Line Items]                          
Accumulated Value   $ 10,000   $ 13,299 $ 13,032 $ 12,377 $ 12,841 $ 13,765 $ 12,008 $ 12,208 $ 11,514 $ 10,979 $ 10,790
C000088012 [Member]                          
Account Value [Line Items]                          
Accumulated Value   10,000   13,567 13,268 12,576 13,021 13,930 12,127 12,305 11,583 11,023 10,812
C000189766 [Member]                          
Account Value [Line Items]                          
Accumulated Value $ 10,000   $ 10,225 12,600 12,334 11,673 12,096 12,937 11,260 11,421 10,736    
C000017686 [Member]                          
Account Value [Line Items]                          
Accumulated Value   9,550   12,388 12,170 11,586 12,051 12,951 11,325 11,543 10,914 10,433 10,279
C000017688 [Member]                          
Account Value [Line Items]                          
Accumulated Value   10,000   12,035 11,925 11,439 11,987 12,980 11,435 11,743 11,175 10,774 10,684
C000017689 [Member]                          
Account Value [Line Items]                          
Accumulated Value   10,000   12,094 11,826 11,503 11,494 12,232 11,486 11,250 10,657 10,556 10,466
C000017691 [Member]                          
Account Value [Line Items]                          
Accumulated Value   10,000   12,339 12,030 11,677 11,645 12,379 11,601 11,340 10,712 10,598 10,477
C000189767 [Member]                          
Account Value [Line Items]                          
Accumulated Value 10,000   10,165 11,862 11,561 11,230 11,195 11,887 11,136 10,883 10,285    
C000088013 [Member]                          
Account Value [Line Items]                          
Accumulated Value   9,550   11,266 11,033 10,758 10,777 11,508 10,823 10,637 10,093 10,031 9,961
C000088014 [Member]                          
Account Value [Line Items]                          
Accumulated Value   10,000   10,945 10,799 10,609 10,718 11,521 10,917 10,810 10,333 10,348 10,353
S&P National AMT-Free Municipal [Member]                          
Account Value [Line Items]                          
Accumulated Value   10,000   12,283 12,085 11,796 11,731 12,507 11,965 11,519 10,844 10,720 10,599
S&P National AMT-Free Municipal (Inception Date 4/10/17) [Member]                          
Account Value [Line Items]                          
Accumulated Value 10,000   10,170 11,653 11,464 11,191 11,129 11,865 11,351 10,928 10,288    
S&P Municipal Bond 50% Investment Grade/50% High Yield [Member]                          
Account Value [Line Items]                          
Accumulated Value   10,000   13,679 13,283 12,644 12,743 13,626 12,358 12,199 11,473 11,043 10,748
S&P Municipal Bond 50% Investment Grade/50% High Yield (Inception Date 4/10/17) [Member]                          
Account Value [Line Items]                          
Accumulated Value 10,000   10,178 12,607 12,242 11,653 11,745 12,558 11,389 11,243 10,574    
S&P Intermediate Term National AMT-Free Municipal [Member]                          
Account Value [Line Items]                          
Accumulated Value   $ 10,000   12,234 11,921 11,665 11,533 12,153 11,723 11,306 10,681 $ 10,621 $ 10,487
S&P Intermediate Term National AMT-Free Municipal (Inception Date 4/10/17) [Member]                          
Account Value [Line Items]                          
Accumulated Value $ 10,000   $ 10,155 $ 11,698 $ 11,399 $ 11,154 $ 11,028 $ 11,621 $ 11,209 $ 10,811 $ 10,214