v3.26.1
Shareholder Report, Average Annual Return (Details)
 12 Months Ended 60 Months Ended 120 Months Ended
Jun. 30, 2026
Jun. 30, 2026
Jun. 30, 2026
Alabama Tax-Free Income Series      
Average Annual Return [Line Items]      
Line Graph and Table Measure Name Alabama Tax-Free Income Series    
Average Annual Return, Percent 8.51% 0.57% 1.73%
Kentucky Tax-Free Income Series      
Average Annual Return [Line Items]      
Line Graph and Table Measure Name Kentucky Tax-Free Income Series    
Average Annual Return, Percent 7.65% 0.81% 1.80%
Mississippi Tax-Free Income Series      
Average Annual Return [Line Items]      
Line Graph and Table Measure Name Mississippi Tax-Free Income Series    
Average Annual Return, Percent 6.93% 0.55% 1.51%
North Carolina Tax-Free Income Series      
Average Annual Return [Line Items]      
Line Graph and Table Measure Name North Carolina Tax-Free Income Series    
Average Annual Return, Percent 7.13% 0.46% 1.50%
Tennessee Tax-Free Income Series      
Average Annual Return [Line Items]      
Line Graph and Table Measure Name Tennessee Tax-Free Income Series    
Average Annual Return, Percent 8.35% 0.89% 1.59%
Intermediate Government Bond Series      
Average Annual Return [Line Items]      
Line Graph and Table Measure Name Intermediate Government Bond Series    
Average Annual Return, Percent 2.35% 1.74% 1.50%
Taxable Municipal Bond Series      
Average Annual Return [Line Items]      
Line Graph and Table Measure Name Taxable Municipal Bond Series    
Average Annual Return, Percent 5.23% (2.38%) 0.55%
Bloomberg Municipal Bond Index [Member]      
Average Annual Return [Line Items]      
Line Graph and Table Measure Name Bloomberg Municipal Bond Index    
Average Annual Return, Percent 7.03% 1.05% 2.14%
Bloomberg Intermediate U.S. Government Bond Index [Member]      
Average Annual Return [Line Items]      
Line Graph and Table Measure Name Bloomberg Intermediate U.S. Government Bond Index    
Average Annual Return, Percent 2.67% 0.91% 1.42%
Bloomberg Taxable Municipal Bond Index [Member]      
Average Annual Return [Line Items]      
Line Graph and Table Measure Name Bloomberg Taxable Municipal Bond Index    
Average Annual Return, Percent 5.13% (0.11%) 2.42%