S000010032 [Member] Annual Fund Operating Expenses - The National Tax-Free Intermediate Bond Fund - Shares |
Oct. 31, 2025 |
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|---|---|---|---|---|
| Prospectus [Line Items] | ||||
| Management Fees (as a percentage of Assets) | 0.30% | [1] | ||
| Other Expenses (as a percentage of Assets): | 0.27% | |||
| Expenses (as a percentage of Assets) | 0.57% | |||
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