v3.25.2
Shareholder Report, Average Annual Return (Details)
 12 Months Ended 60 Months Ended 120 Months Ended
Jun. 30, 2025
Jun. 30, 2025
Jun. 30, 2025
C000006121 [Member]      
Average Annual Return [Line Items]      
Line Graph and Table Measure Name Institutional Shares    
Average Annual Return, Percent 0.68% 0.49% 1.94%
C000100249 [Member]      
Average Annual Return [Line Items]      
Line Graph and Table Measure Name Service Shares    
Average Annual Return, Percent 0.43% 0.23% 1.70%
C000006118 [Member]      
Average Annual Return [Line Items]      
Line Graph and Table Measure Name Investor A Shares (with sales charge)    
Average Annual Return, Percent (3.94%) (0.64%) 1.25%
C000038033 [Member]      
Average Annual Return [Line Items]      
Line Graph and Table Measure Name Investor C Shares (with sales charge)    
Average Annual Return, Percent (1.39%) (0.52%) 1.09%
C000100250 [Member]      
Average Annual Return [Line Items]      
Line Graph and Table Measure Name Class K Shares    
Average Annual Return, Percent 0.73% 0.53% 1.99%
C000006125 [Member]      
Average Annual Return [Line Items]      
Line Graph and Table Measure Name Institutional Shares    
Average Annual Return, Percent 4.02% 1.51% 1.33%
C000038034 [Member]      
Average Annual Return [Line Items]      
Line Graph and Table Measure Name Investor A Shares (with sales charge)    
Average Annual Return, Percent 0.56% 0.63% 0.76%
C000006122 [Member]      
Average Annual Return [Line Items]      
Line Graph and Table Measure Name Investor A1 Shares    
Average Annual Return, Percent 3.91% 1.41% 1.22%
C000006124 [Member]      
Average Annual Return [Line Items]      
Line Graph and Table Measure Name Investor C Shares (with sales charge)    
Average Annual Return, Percent 1.90% 0.48% 0.46%
C000038035 [Member]      
Average Annual Return [Line Items]      
Line Graph and Table Measure Name Class K Shares    
Average Annual Return, Percent 4.07% 1.56% 1.37%
Without Sales Load [Member] | C000006118 [Member]      
Average Annual Return [Line Items]      
Line Graph and Table Measure Name Investor A Shares    
Average Annual Return, Percent 0.33% 0.23% 1.69%
Without Sales Load [Member] | C000038033 [Member]      
Average Annual Return [Line Items]      
Line Graph and Table Measure Name Investor C Shares    
Average Annual Return, Percent (0.42%) (0.52%) 1.09%
Without Sales Load [Member] | C000038034 [Member]      
Average Annual Return [Line Items]      
Line Graph and Table Measure Name Investor A Shares    
Average Annual Return, Percent 3.66% 1.25% 1.07%
Without Sales Load [Member] | C000006124 [Member]      
Average Annual Return [Line Items]      
Line Graph and Table Measure Name Investor C Shares    
Average Annual Return, Percent 2.90% 0.48% 0.46%
Bloomberg Municipal Bond Index [Member]      
Average Annual Return [Line Items]      
Line Graph and Table Measure Name Bloomberg Municipal Bond Index    
Average Annual Return, Percent 1.11% 0.51% 2.20%
Bloomberg Municipal 1 5 Year Index [Member]      
Average Annual Return [Line Items]      
Line Graph and Table Measure Name Bloomberg Municipal 1-5 Year Index    
Average Annual Return, Percent 4.01% 1.16% 1.55%
Short Term Customized Reference Benchmark [Member]      
Average Annual Return [Line Items]      
Line Graph and Table Measure Name Short-Term Customized Reference Benchmark    
Average Annual Return, Percent 3.88% 1.33%