v3.26.1
Shareholder Report, Average Annual Return (Details)
 12 Months Ended 60 Months Ended 63 Months Ended 120 Months Ended
May 31, 2026
May 31, 2026
May 31, 2026
May 31, 2026
Without Sales Load [Member] | C000005536        
Average Annual Return [Line Items]        
Average Annual Return, Percent 4.23% 2.22%   2.35%
Without Sales Load [Member] | C000005537        
Average Annual Return [Line Items]        
Average Annual Return, Percent 3.67% 1.88%   2.04%
Without Sales Load [Member] | C000166333        
Average Annual Return [Line Items]        
Average Annual Return, Percent 4.39% 2.36%   2.46%
Without Sales Load [Member] | C000225824        
Average Annual Return [Line Items]        
Average Annual Return, Percent 4.73% 2.70% 2.61%  
Bloomberg U.S. Aggregate Bond Index        
Average Annual Return [Line Items]        
Average Annual Return, Percent 5.13% 0.17%   1.70%
Bloomberg U.S. Aggregate Bond Index        
Average Annual Return [Line Items]        
Average Annual Return, Percent 5.13% 0.17%   1.70%
Bloomberg U.S. Aggregate Bond Index        
Average Annual Return [Line Items]        
Average Annual Return, Percent 5.13% 0.17%   1.70%
Bloomberg U.S. Aggregate Bond Index        
Average Annual Return [Line Items]        
Average Annual Return, Percent 5.13% 0.17% 0.12%  
Bloomberg 1-3 Year U.S. Government/Credit Bond Index        
Average Annual Return [Line Items]        
Average Annual Return, Percent 3.72% 2.08%   2.05%
Bloomberg 1-3 Year U.S. Government/Credit Bond Index        
Average Annual Return [Line Items]        
Average Annual Return, Percent 3.72% 2.08%   2.05%
Bloomberg 1-3 Year U.S. Government/Credit Bond Index        
Average Annual Return [Line Items]        
Average Annual Return, Percent 3.72% 2.08%   2.05%
Bloomberg 1-3 Year U.S. Government/Credit Bond Index        
Average Annual Return [Line Items]        
Average Annual Return, Percent 3.72% 2.08% 1.99%