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S000010032 [Member] Average Annual Total Returns
 12 Months Ended 60 Months Ended 120 Months Ended
Dec. 31, 2025
Dec. 31, 2025
Dec. 31, 2025
Bloomberg Municipal Bond Index      
Prospectus [Line Items]      
Average Annual Return, Percent [1] 4.25% 0.80% 2.34%
Bloomberg 3-15 Year Blend Municipal Bond Index      
Prospectus [Line Items]      
Average Annual Return, Percent [2] 5.30% 1.10% 2.34%
Shares      
Prospectus [Line Items]      
Average Annual Return, Percent 5.09% 0.71% 2.02%
Shares | After Taxes on Distributions      
Prospectus [Line Items]      
Average Annual Return, Percent 5.01% 0.62% 1.92%
Shares | After Taxes on Distributions and Sales      
Prospectus [Line Items]      
Average Annual Return, Percent 4.09% 0.98% 2.00%
[1] The Bloomberg Municipal Bond Index is an unmanaged index that measures the U.S. Dollar-denominated long-term tax exempt bond market. The Index figures do not reflect any deduction for fees, taxes or expenses.
[2] The Bloomberg 3‑15 Year Blend Municipal Bond Index is an unmanaged index comprised of investment-grade municipal securities ranging from 2 to 17 years in maturity. The Index figures do not reflect any deduction for fees, taxes or expenses.