S000012096 [Member] Average Annual Total Returns	3 Months Ended	12 Months Ended	60 Months Ended	120 Months Ended	146 Months Ended	293 Months Ended	466 Months Ended
S000012096 [Member] Average Annual Total Returns	Dec. 31, 2024	Dec. 31, 2024	Dec. 31, 2024	Dec. 31, 2024	Dec. 31, 2024	Dec. 31, 2024	Dec. 31, 2024
Blended Benchmark (consisting of 85% Bloomberg U.S. Corporate Bond Index and 15% ICE BofA U.S. Cash Pay High Yield Constrained Index)
Prospectus [Line Items]
Average Annual Return, Percent		3.00%	0.87%	2.84%
Bloomberg U.S. Corporate Bond Index (reflects no deductions for fees, expenses or taxes)
Prospectus [Line Items]
Average Annual Return, Percent		2.13%	0.30%	2.43%
Bloomberg U.S. Aggregate Bond Index (reflects no deductions for fees, expenses or taxes)
Prospectus [Line Items]
Average Annual Return, Percent		1.25%	(0.33%)	1.35%
C000122679 [Member]
Prospectus [Line Items]
Average Annual Return, Percent		2.81%	1.16%	2.80%
Performance Inception Date					Nov. 08, 2012
C000255091 [Member]
Prospectus [Line Items]
Average Annual Return, Percent		2.79%	1.07%	2.70%
Performance Inception Date	Oct. 02, 2024
C000032979 [Member]
Prospectus [Line Items]
Average Annual Return, Percent		(2.35%)	(0.18%)	1.93%
Performance Inception Date						Jul. 31, 2000
C000032979 [Member] \| After Taxes on Distributions
Prospectus [Line Items]
Average Annual Return, Percent		(3.99%)	(1.76%)	0.52%
Performance Inception Date						Jul. 31, 2000
C000032979 [Member] \| After Taxes on Distributions and Sales
Prospectus [Line Items]
Average Annual Return, Percent		(1.40%)	(0.69%)	0.91%
Performance Inception Date						Jul. 31, 2000
C000032982 [Member]
Prospectus [Line Items]
Average Annual Return, Percent		2.79%	1.07%	2.70%
Performance Inception Date							Mar. 05, 1986
C000122677 [Member]
Prospectus [Line Items]
Average Annual Return, Percent		2.86%	1.21%	2.84%
Performance Inception Date					Nov. 08, 2012