S000010032 [Member] Expense Example - The National Tax-Free Intermediate Bond Fund - Shares	Oct. 31, 2025 USD ($)
Prospectus [Line Items]
Expense Example, with Redemption, 1 Year	$ 58
Expense Example, with Redemption, 3 Years	183
Expense Example, with Redemption, 5 Years	318
Expense Example, with Redemption, 10 Years	$ 714

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