v3.25.2
Shareholder Report, Average Annual Return (Details)
 12 Months Ended 51 Months Ended 60 Months Ended 113 Months Ended 120 Months Ended
May 31, 2025
May 31, 2025
May 31, 2025
May 31, 2025
May 31, 2025
Without Sales Load [Member] | C000005536          
Average Annual Return [Line Items]          
Average Annual Return, Percent 6.07%   2.04%   1.99%
Without Sales Load [Member] | C000005537          
Average Annual Return [Line Items]          
Average Annual Return, Percent 5.73%   1.74%   1.73%
Without Sales Load [Member] | C000166333          
Average Annual Return [Line Items]          
Average Annual Return, Percent 5.98%   2.11% 2.27%  
Without Sales Load [Member] | C000225824          
Average Annual Return [Line Items]          
Average Annual Return, Percent 6.56% 2.12%      
Bloomberg U.S. Aggregate Bond Index          
Average Annual Return [Line Items]          
Average Annual Return, Percent 5.46%   (0.90%)   1.49%
Bloomberg U.S. Aggregate Bond Index          
Average Annual Return [Line Items]          
Average Annual Return, Percent 5.46%   (0.90%)   1.49%
Bloomberg U.S. Aggregate Bond Index          
Average Annual Return [Line Items]          
Average Annual Return, Percent 5.46%   (0.90%) 1.61%  
Bloomberg U.S. Aggregate Bond Index          
Average Annual Return [Line Items]          
Average Annual Return, Percent 5.46% (1.02%)      
Bloomberg 1-3 Year U.S. Government/Credit Bond Index          
Average Annual Return [Line Items]          
Average Annual Return, Percent 5.85%   1.49%   1.78%
Bloomberg 1-3 Year U.S. Government/Credit Bond Index          
Average Annual Return [Line Items]          
Average Annual Return, Percent 5.85%   1.49%   1.78%
Bloomberg 1-3 Year U.S. Government/Credit Bond Index          
Average Annual Return [Line Items]          
Average Annual Return, Percent 5.85%   1.49% 1.89%  
Bloomberg 1-3 Year U.S. Government/Credit Bond Index          
Average Annual Return [Line Items]          
Average Annual Return, Percent 5.85% 1.59%