v3.26.1
Shareholder Report, Holdings (Details)
Mar. 31, 2026
C000001504 [Member] | N A not applicable [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.10% [1]
C000001504 [Member] | N R not rated [Member]  
Holdings [Line Items]  
Percent of Total Investments 8.00% [1]
C000001504 [Member] | Standard & Poor's, BBB Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 8.50% [1]
C000001504 [Member] | Standard & Poor's, A Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 23.70% [1]
C000001504 [Member] | Standard & Poor's, AA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 39.60% [1]
C000001504 [Member] | Standard & Poor's, AAA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 16.70% [1]
C000001504 [Member] | BB or Lower [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.40% [1]
C000001504 [Member] | Variable Rate Senior Loan Interests [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.00%
C000001504 [Member] | Collateralized Mortgage-Backed Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.60%
C000001504 [Member] | Exchange Traded Funds [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.10% [2]
C000001504 [Member] | Municipal Bonds [Member]  
Holdings [Line Items]  
Percent of Total Investments 99.30%
C000137699 [Member] | N A not applicable [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.10% [3]
C000137699 [Member] | N R not rated [Member]  
Holdings [Line Items]  
Percent of Total Investments 8.00% [3]
C000137699 [Member] | Standard & Poor's, BBB Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 8.50% [3]
C000137699 [Member] | Standard & Poor's, A Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 23.70% [3]
C000137699 [Member] | Standard & Poor's, AA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 39.60% [3]
C000137699 [Member] | Standard & Poor's, AAA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 16.70% [3]
C000137699 [Member] | BB or Lower [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.40% [3]
C000137699 [Member] | Variable Rate Senior Loan Interests [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.00%
C000137699 [Member] | Collateralized Mortgage-Backed Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.60%
C000137699 [Member] | Exchange Traded Funds [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.10% [4]
C000137699 [Member] | Municipal Bonds [Member]  
Holdings [Line Items]  
Percent of Total Investments 99.30%
C000000699 [Member] | N A not applicable [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.10% [5]
C000000699 [Member] | N R not rated [Member]  
Holdings [Line Items]  
Percent of Total Investments 8.00% [5]
C000000699 [Member] | Standard & Poor's, BBB Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 8.50% [5]
C000000699 [Member] | Standard & Poor's, A Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 23.70% [5]
C000000699 [Member] | Standard & Poor's, AA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 39.60% [5]
C000000699 [Member] | Standard & Poor's, AAA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 16.70% [5]
C000000699 [Member] | BB or Lower [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.40% [5]
C000000699 [Member] | Variable Rate Senior Loan Interests [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.00%
C000000699 [Member] | Collateralized Mortgage-Backed Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.60%
C000000699 [Member] | Exchange Traded Funds [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.10% [6]
C000000699 [Member] | Municipal Bonds [Member]  
Holdings [Line Items]  
Percent of Total Investments 99.30%
C000000700 [Member] | N A not applicable [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.80% [7],[8]
C000000700 [Member] | N R not rated [Member]  
Holdings [Line Items]  
Percent of Total Investments 12.70% [7],[8]
C000000700 [Member] | Standard & Poor's, BBB Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 13.40% [7],[8]
C000000700 [Member] | Standard & Poor's, A Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 23.40% [7],[8]
C000000700 [Member] | Standard & Poor's, AA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 36.30% [7],[8]
C000000700 [Member] | Standard & Poor's, AAA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 8.00% [7],[8]
C000000700 [Member] | BB or Lower [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.40% [7],[8]
C000000700 [Member] | Variable Rate Senior Loan Interests [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.00% [8]
C000000700 [Member] | Exchange Traded Funds [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.80% [8],[9]
C000000700 [Member] | Municipal Bonds [Member]  
Holdings [Line Items]  
Percent of Total Investments 99.20% [8]
C000000700 [Member] | Warrant [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.00% [8]
C000137700 [Member] | N A not applicable [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.80% [10],[11]
C000137700 [Member] | N R not rated [Member]  
Holdings [Line Items]  
Percent of Total Investments 12.70% [10],[11]
C000137700 [Member] | Standard & Poor's, BBB Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 13.40% [10],[11]
C000137700 [Member] | Standard & Poor's, A Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 23.40% [10],[11]
C000137700 [Member] | Standard & Poor's, AA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 36.30% [10],[11]
C000137700 [Member] | Standard & Poor's, AAA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 8.00% [10],[11]
C000137700 [Member] | BB or Lower [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.40% [10],[11]
C000137700 [Member] | Variable Rate Senior Loan Interests [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.00% [11]
C000137700 [Member] | Exchange Traded Funds [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.80% [11],[12]
C000137700 [Member] | Municipal Bonds [Member]  
Holdings [Line Items]  
Percent of Total Investments 99.20% [11]
C000137700 [Member] | Warrant [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.00% [11]
C000171394 [Member] | N A not applicable [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.80% [13],[14]
C000171394 [Member] | N R not rated [Member]  
Holdings [Line Items]  
Percent of Total Investments 12.70% [13],[14]
C000171394 [Member] | Standard & Poor's, BBB Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 13.40% [13],[14]
C000171394 [Member] | Standard & Poor's, A Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 23.40% [13],[14]
C000171394 [Member] | Standard & Poor's, AA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 36.30% [13],[14]
C000171394 [Member] | Standard & Poor's, AAA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 8.00% [13],[14]
C000171394 [Member] | BB or Lower [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.40% [13],[14]
C000171394 [Member] | Variable Rate Senior Loan Interests [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.00% [14]
C000171394 [Member] | Exchange Traded Funds [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.80% [14],[15]
C000171394 [Member] | Municipal Bonds [Member]  
Holdings [Line Items]  
Percent of Total Investments 99.20% [14]
C000171394 [Member] | Warrant [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.00% [14]
C000001507 [Member] | N A not applicable [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.80% [16],[17]
C000001507 [Member] | N R not rated [Member]  
Holdings [Line Items]  
Percent of Total Investments 12.70% [16],[17]
C000001507 [Member] | Standard & Poor's, BBB Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 13.40% [16],[17]
C000001507 [Member] | Standard & Poor's, A Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 23.40% [16],[17]
C000001507 [Member] | Standard & Poor's, AA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 36.30% [16],[17]
C000001507 [Member] | Standard & Poor's, AAA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 8.00% [16],[17]
C000001507 [Member] | BB or Lower [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.40% [16],[17]
C000001507 [Member] | Variable Rate Senior Loan Interests [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.00% [17]
C000001507 [Member] | Exchange Traded Funds [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.80% [17],[18]
C000001507 [Member] | Municipal Bonds [Member]  
Holdings [Line Items]  
Percent of Total Investments 99.20% [17]
C000001507 [Member] | Warrant [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.00% [17]
C000001512 [Member] | N R not rated [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.20% [19]
C000001512 [Member] | Standard & Poor's, BBB Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 6.70% [19]
C000001512 [Member] | Standard & Poor's, A Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 22.80% [19]
C000001512 [Member] | Standard & Poor's, AA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 44.00% [19]
C000001512 [Member] | Standard & Poor's, AAA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 19.70% [19]
C000001512 [Member] | BB or Lower [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.60% [19]
C000001512 [Member] | Municipal Bonds [Member]  
Holdings [Line Items]  
Percent of Total Investments 100.00%
C000137701 [Member] | N R not rated [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.20% [20]
C000137701 [Member] | Standard & Poor's, BBB Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 6.70% [20]
C000137701 [Member] | Standard & Poor's, A Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 22.80% [20]
C000137701 [Member] | Standard & Poor's, AA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 44.00% [20]
C000137701 [Member] | Standard & Poor's, AAA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 19.70% [20]
C000137701 [Member] | BB or Lower [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.60% [20]
C000137701 [Member] | Municipal Bonds [Member]  
Holdings [Line Items]  
Percent of Total Investments 100.00%
C000000702 [Member] | N R not rated [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.20% [21]
C000000702 [Member] | Standard & Poor's, BBB Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 6.70% [21]
C000000702 [Member] | Standard & Poor's, A Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 22.80% [21]
C000000702 [Member] | Standard & Poor's, AA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 44.00% [21]
C000000702 [Member] | Standard & Poor's, AAA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 19.70% [21]
C000000702 [Member] | BB or Lower [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.60% [21]
C000000702 [Member] | Municipal Bonds [Member]  
Holdings [Line Items]  
Percent of Total Investments 100.00%
C000000703 [Member] | N A not applicable [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.00% [22],[23]
C000000703 [Member] | N R not rated [Member]  
Holdings [Line Items]  
Percent of Total Investments 49.40% [22],[23]
C000000703 [Member] | Standard & Poor's, BBB Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 7.60% [22],[23]
C000000703 [Member] | Standard & Poor's, A Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 16.00% [22],[23]
C000000703 [Member] | Standard & Poor's, AA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 16.40% [22],[23]
C000000703 [Member] | Standard & Poor's, AAA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.20% [22],[23]
C000000703 [Member] | BB or Lower [Member]  
Holdings [Line Items]  
Percent of Total Investments 7.40% [22],[23]
C000000703 [Member] | Variable Rate Senior Loan Interests [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.00% [23]
C000000703 [Member] | Exchange Traded Funds [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.10% [23],[24]
C000000703 [Member] | Municipal Bonds [Member]  
Holdings [Line Items]  
Percent of Total Investments 98.90% [23]
C000000703 [Member] | Corporate Bond Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.10% [23]
C000000703 [Member] | Repurchase Agreements [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.90% [23]
C000000703 [Member] | Common Stock [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.00% [23]
C000000703 [Member] | Investments Purchased with Collateral from Securities Lending [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.00% [23]
C000137702 [Member] | N A not applicable [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.00% [25],[26]
C000137702 [Member] | N R not rated [Member]  
Holdings [Line Items]  
Percent of Total Investments 49.40% [25],[26]
C000137702 [Member] | Standard & Poor's, BBB Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 7.60% [25],[26]
C000137702 [Member] | Standard & Poor's, A Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 16.00% [25],[26]
C000137702 [Member] | Standard & Poor's, AA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 16.40% [25],[26]
C000137702 [Member] | Standard & Poor's, AAA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.20% [25],[26]
C000137702 [Member] | BB or Lower [Member]  
Holdings [Line Items]  
Percent of Total Investments 7.40% [25],[26]
C000137702 [Member] | Variable Rate Senior Loan Interests [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.00% [26]
C000137702 [Member] | Exchange Traded Funds [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.10% [26],[27]
C000137702 [Member] | Municipal Bonds [Member]  
Holdings [Line Items]  
Percent of Total Investments 98.90% [26]
C000137702 [Member] | Corporate Bond Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.10% [26]
C000137702 [Member] | Repurchase Agreements [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.90% [26]
C000137702 [Member] | Common Stock [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.00% [26]
C000137702 [Member] | Investments Purchased with Collateral from Securities Lending [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.00% [26]
C000171395 [Member] | N A not applicable [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.00% [28],[29]
C000171395 [Member] | N R not rated [Member]  
Holdings [Line Items]  
Percent of Total Investments 49.40% [28],[29]
C000171395 [Member] | Standard & Poor's, BBB Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 7.60% [28],[29]
C000171395 [Member] | Standard & Poor's, A Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 16.00% [28],[29]
C000171395 [Member] | Standard & Poor's, AA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 16.40% [28],[29]
C000171395 [Member] | Standard & Poor's, AAA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.20% [28],[29]
C000171395 [Member] | BB or Lower [Member]  
Holdings [Line Items]  
Percent of Total Investments 7.40% [28],[29]
C000171395 [Member] | Variable Rate Senior Loan Interests [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.00% [29]
C000171395 [Member] | Exchange Traded Funds [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.10% [29],[30]
C000171395 [Member] | Municipal Bonds [Member]  
Holdings [Line Items]  
Percent of Total Investments 98.90% [29]
C000171395 [Member] | Corporate Bond Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.10% [29]
C000171395 [Member] | Repurchase Agreements [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.90% [29]
C000171395 [Member] | Common Stock [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.00% [29]
C000171395 [Member] | Investments Purchased with Collateral from Securities Lending [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.00% [29]
C000001515 [Member] | N A not applicable [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.00% [31],[32]
C000001515 [Member] | N R not rated [Member]  
Holdings [Line Items]  
Percent of Total Investments 49.40% [31],[32]
C000001515 [Member] | Standard & Poor's, BBB Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 7.60% [31],[32]
C000001515 [Member] | Standard & Poor's, A Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 16.00% [31],[32]
C000001515 [Member] | Standard & Poor's, AA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 16.40% [31],[32]
C000001515 [Member] | Standard & Poor's, AAA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.20% [31],[32]
C000001515 [Member] | BB or Lower [Member]  
Holdings [Line Items]  
Percent of Total Investments 7.40% [31],[32]
C000001515 [Member] | Variable Rate Senior Loan Interests [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.00% [32]
C000001515 [Member] | Exchange Traded Funds [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.10% [32],[33]
C000001515 [Member] | Municipal Bonds [Member]  
Holdings [Line Items]  
Percent of Total Investments 98.90% [32]
C000001515 [Member] | Corporate Bond Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.10% [32]
C000001515 [Member] | Repurchase Agreements [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.90% [32]
C000001515 [Member] | Common Stock [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.00% [32]
C000001515 [Member] | Investments Purchased with Collateral from Securities Lending [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.00% [32]
C000001515 [Member] | Repurchase Agreements Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.90% [32]
C000122986 [Member] | N A not applicable [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.70% [34],[35]
C000122986 [Member] | N R not rated [Member]  
Holdings [Line Items]  
Percent of Total Investments 54.20% [34],[35]
C000122986 [Member] | Standard & Poor's, BBB Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 11.90% [34],[35]
C000122986 [Member] | Standard & Poor's, A Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 12.50% [34],[35]
C000122986 [Member] | Standard & Poor's, AA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.50% [34],[35]
C000122986 [Member] | Standard & Poor's, AAA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.10% [34],[35]
C000122986 [Member] | BB or Lower [Member]  
Holdings [Line Items]  
Percent of Total Investments 15.10% [34],[35]
C000122986 [Member] | Variable Rate Senior Loan Interests [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.00% [35]
C000122986 [Member] | Exchange Traded Funds [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.60% [35],[36]
C000122986 [Member] | Municipal Bonds [Member]  
Holdings [Line Items]  
Percent of Total Investments 97.10% [35]
C000122986 [Member] | Warrant [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.00% [35]
C000122986 [Member] | Corporate Bond Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.20% [35]
C000122986 [Member] | Repurchase Agreements [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.10% [35]
C000122986 [Member] | Common Stock [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.00% [35]
C000137704 [Member] | N A not applicable [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.70% [37],[38]
C000137704 [Member] | N R not rated [Member]  
Holdings [Line Items]  
Percent of Total Investments 54.20% [37],[38]
C000137704 [Member] | Standard & Poor's, BBB Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 11.90% [37],[38]
C000137704 [Member] | Standard & Poor's, A Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 12.50% [37],[38]
C000137704 [Member] | Standard & Poor's, AA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.50% [37],[38]
C000137704 [Member] | Standard & Poor's, AAA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.10% [37],[38]
C000137704 [Member] | BB or Lower [Member]  
Holdings [Line Items]  
Percent of Total Investments 15.10% [37],[38]
C000137704 [Member] | Variable Rate Senior Loan Interests [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.00% [38]
C000137704 [Member] | Exchange Traded Funds [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.60% [38],[39]
C000137704 [Member] | Municipal Bonds [Member]  
Holdings [Line Items]  
Percent of Total Investments 97.10% [38]
C000137704 [Member] | Warrant [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.00% [38]
C000137704 [Member] | Corporate Bond Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.20% [38]
C000137704 [Member] | Repurchase Agreements [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.10% [38]
C000137704 [Member] | Common Stock [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.00% [38]
C000122984 [Member] | N A not applicable [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.70% [40],[41]
C000122984 [Member] | N R not rated [Member]  
Holdings [Line Items]  
Percent of Total Investments 54.20% [40],[41]
C000122984 [Member] | Standard & Poor's, BBB Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 11.90% [40],[41]
C000122984 [Member] | Standard & Poor's, A Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 12.50% [40],[41]
C000122984 [Member] | Standard & Poor's, AA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.50% [40],[41]
C000122984 [Member] | Standard & Poor's, AAA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.10% [40],[41]
C000122984 [Member] | BB or Lower [Member]  
Holdings [Line Items]  
Percent of Total Investments 15.10% [40],[41]
C000122984 [Member] | Variable Rate Senior Loan Interests [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.00% [41]
C000122984 [Member] | Exchange Traded Funds [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.60% [41],[42]
C000122984 [Member] | Municipal Bonds [Member]  
Holdings [Line Items]  
Percent of Total Investments 97.10% [41]
C000122984 [Member] | Warrant [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.00% [41]
C000122984 [Member] | Corporate Bond Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.20% [41]
C000122984 [Member] | Repurchase Agreements [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.10% [41]
C000122984 [Member] | Common Stock [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.00% [41]
C000149455 [Member] | N A not applicable [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.00% [43],[44]
C000149455 [Member] | N R not rated [Member]  
Holdings [Line Items]  
Percent of Total Investments 35.20% [43],[44]
C000149455 [Member] | Standard & Poor's, BBB Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 13.50% [43],[44]
C000149455 [Member] | Standard & Poor's, A Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 20.10% [43],[44]
C000149455 [Member] | Standard & Poor's, AA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 19.80% [43],[44]
C000149455 [Member] | Standard & Poor's, AAA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.40% [43],[44]
C000149455 [Member] | BB or Lower [Member]  
Holdings [Line Items]  
Percent of Total Investments 6.00% [43],[44]
C000149455 [Member] | Variable Rate Senior Loan Interests [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.00% [44]
C000149455 [Member] | Municipal Bonds [Member]  
Holdings [Line Items]  
Percent of Total Investments 100.00% [44]
C000149455 [Member] | Warrant [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.00% [44]
C000149455 [Member] | Corporate Bond Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.00% [44]
C000149455 [Member] | Common Stock [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.00% [44]
C000149456 [Member] | N A not applicable [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.00% [45],[46]
C000149456 [Member] | N R not rated [Member]  
Holdings [Line Items]  
Percent of Total Investments 35.20% [45],[46]
C000149456 [Member] | Standard & Poor's, BBB Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 13.50% [45],[46]
C000149456 [Member] | Standard & Poor's, A Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 20.10% [45],[46]
C000149456 [Member] | Standard & Poor's, AA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 19.80% [45],[46]
C000149456 [Member] | Standard & Poor's, AAA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.40% [45],[46]
C000149456 [Member] | BB or Lower [Member]  
Holdings [Line Items]  
Percent of Total Investments 6.00% [45],[46]
C000149456 [Member] | Variable Rate Senior Loan Interests [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.00% [46]
C000149456 [Member] | Municipal Bonds [Member]  
Holdings [Line Items]  
Percent of Total Investments 100.00% [46]
C000149456 [Member] | Warrant [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.00% [46]
C000149456 [Member] | Corporate Bond Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.00% [46]
C000149456 [Member] | Common Stock [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.00% [46]
C000149457 [Member] | N A not applicable [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.00% [47],[48]
C000149457 [Member] | N R not rated [Member]  
Holdings [Line Items]  
Percent of Total Investments 35.20% [47],[48]
C000149457 [Member] | Standard & Poor's, BBB Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 13.50% [47],[48]
C000149457 [Member] | Standard & Poor's, A Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 20.10% [47],[48]
C000149457 [Member] | Standard & Poor's, AA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 19.80% [47],[48]
C000149457 [Member] | Standard & Poor's, AAA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.40% [47],[48]
C000149457 [Member] | BB or Lower [Member]  
Holdings [Line Items]  
Percent of Total Investments 6.00% [47],[48]
C000149457 [Member] | Variable Rate Senior Loan Interests [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.00% [48]
C000149457 [Member] | Municipal Bonds [Member]  
Holdings [Line Items]  
Percent of Total Investments 100.00% [48]
C000149457 [Member] | Warrant [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.00% [48]
C000149457 [Member] | Corporate Bond Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.00% [48]
C000149457 [Member] | Common Stock [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.00% [48]
[1] The ratings disclosed are the highest rating given by one of the following national rating agencies: Standard & Poor’s (S&P), Moody’s Investors Service, Inc. (Moody’s) or Fitch, Inc (Fitch). This treatment of split-rated securities may differ from that used for other purposes, such as for Fund investment policies. Credit ratings are subject to change. AAA, AA, A, and BBB are investment grade ratings; BB, B, CCC, CC, C and D are below-investment grade ratings. Holdings designated N/R are not rated by these national ratings agencies.
[2] Affiliated investment.
[3] The ratings disclosed are the highest rating given by one of the following national rating agencies: Standard & Poor’s (S&P), Moody’s Investors Service, Inc. (Moody’s) or Fitch, Inc (Fitch). This treatment of split-rated securities may differ from that used for other purposes, such as for Fund investment policies. Credit ratings are subject to change. AAA, AA, A, and BBB are investment grade ratings; BB, B, CCC, CC, C and D are below-investment grade ratings. Holdings designated N/R are not rated by these national ratings agencies.
[4] Affiliated investment.
[5] The ratings disclosed are the highest rating given by one of the following national rating agencies: Standard & Poor’s (S&P), Moody’s Investors Service, Inc. (Moody’s) or Fitch, Inc (Fitch). This treatment of split-rated securities may differ from that used for other purposes, such as for Fund investment policies. Credit ratings are subject to change. AAA, AA, A, and BBB are investment grade ratings; BB, B, CCC, CC, C and D are below-investment grade ratings. Holdings designated N/R are not rated by these national ratings agencies.
[6] Affiliated investment.
[7] The ratings disclosed are the highest rating given by one of the following national rating agencies: Standard & Poor’s (S&P), Moody’s Investors Service, Inc. (Moody’s) or Fitch, Inc (Fitch). This treatment of split-rated securities may differ from that used for other purposes, such as for Fund investment policies. Credit ratings are subject to change. AAA, AA, A, and BBB are investment grade ratings; BB, B, CCC, CC, C and D are below-investment grade ratings. Holdings designated N/R are not rated by these national ratings agencies.
[8] Total investments include the Fund’s assets attributable to financial leverage. For these purposes, financial leverage includes the Fund’s investments in the residual interest certificates (also called inverse floating rate securities) in tender option bond (TOB) trusts, including the portion of assets held by a TOB trust that has been effectively financed by the trust’s issuance of floating rate securities.
[9] Affiliated investment.
[10] The ratings disclosed are the highest rating given by one of the following national rating agencies: Standard & Poor’s (S&P), Moody’s Investors Service, Inc. (Moody’s) or Fitch, Inc (Fitch). This treatment of split-rated securities may differ from that used for other purposes, such as for Fund investment policies. Credit ratings are subject to change. AAA, AA, A, and BBB are investment grade ratings; BB, B, CCC, CC, C and D are below-investment grade ratings. Holdings designated N/R are not rated by these national ratings agencies.
[11] Total investments include the Fund’s assets attributable to financial leverage. For these purposes, financial leverage includes the Fund’s investments in the residual interest certificates (also called inverse floating rate securities) in tender option bond (TOB) trusts, including the portion of assets held by a TOB trust that has been effectively financed by the trust’s issuance of floating rate securities.
[12] Affiliated investment.
[13] The ratings disclosed are the highest rating given by one of the following national rating agencies: Standard & Poor’s (S&P), Moody’s Investors Service, Inc. (Moody’s) or Fitch, Inc (Fitch). This treatment of split-rated securities may differ from that used for other purposes, such as for Fund investment policies. Credit ratings are subject to change. AAA, AA, A, and BBB are investment grade ratings; BB, B, CCC, CC, C and D are below-investment grade ratings. Holdings designated N/R are not rated by these national ratings agencies.
[14] Total investments include the Fund’s assets attributable to financial leverage. For these purposes, financial leverage includes the Fund’s investments in the residual interest certificates (also called inverse floating rate securities) in tender option bond (TOB) trusts, including the portion of assets held by a TOB trust that has been effectively financed by the trust’s issuance of floating rate securities.
[15] Affiliated investment.
[16] The ratings disclosed are the highest rating given by one of the following national rating agencies: Standard & Poor’s (S&P), Moody’s Investors Service, Inc. (Moody’s) or Fitch, Inc (Fitch). This treatment of split-rated securities may differ from that used for other purposes, such as for Fund investment policies. Credit ratings are subject to change. AAA, AA, A, and BBB are investment grade ratings; BB, B, CCC, CC, C and D are below-investment grade ratings. Holdings designated N/R are not rated by these national ratings agencies.
[17] Total investments include the Fund’s assets attributable to financial leverage. For these purposes, financial leverage includes the Fund’s investments in the residual interest certificates (also called inverse floating rate securities) in tender option bond (TOB) trusts, including the portion of assets held by a TOB trust that has been effectively financed by the trust’s issuance of floating rate securities.
[18] Affiliated investment.
[19] The ratings disclosed are the highest rating given by one of the following national rating agencies: Standard & Poor’s (S&P), Moody’s Investors Service, Inc. (Moody’s) or Fitch, Inc (Fitch). This treatment of split-rated securities may differ from that used for other purposes, such as for Fund investment policies. Credit ratings are subject to change. AAA, AA, A, and BBB are investment grade ratings; BB, B, CCC, CC, C and D are below-investment grade ratings. Holdings designated N/R are not rated by these national ratings agencies.
[20] The ratings disclosed are the highest rating given by one of the following national rating agencies: Standard & Poor’s (S&P), Moody’s Investors Service, Inc. (Moody’s) or Fitch, Inc (Fitch). This treatment of split-rated securities may differ from that used for other purposes, such as for Fund investment policies. Credit ratings are subject to change. AAA, AA, A, and BBB are investment grade ratings; BB, B, CCC, CC, C and D are below-investment grade ratings. Holdings designated N/R are not rated by these national ratings agencies.
[21] The ratings disclosed are the highest rating given by one of the following national rating agencies: Standard & Poor’s (S&P), Moody’s Investors Service, Inc. (Moody’s) or Fitch, Inc (Fitch). This treatment of split-rated securities may differ from that used for other purposes, such as for Fund investment policies. Credit ratings are subject to change. AAA, AA, A, and BBB are investment grade ratings; BB, B, CCC, CC, C and D are below-investment grade ratings. Holdings designated N/R are not rated by these national ratings agencies.
[22] The ratings disclosed are the lowest rating given by one of the following national rating agencies: Standard & Poor’s (S&P), Moody’s Investors Service, Inc. (Moody’s) or Fitch, Inc (Fitch). This treatment of split-rated securities may differ from that used for other purposes, such as for Fund investment policies. Credit ratings are subject to change. AAA, AA, A, and BBB are investment grade ratings; BB, B, CCC, CC, C and D are below-investment grade ratings. Holdings designated N/R are not rated by these national ratings agencies.
[23] Total investments include the Fund’s assets attributable to financial leverage. For these purposes, financial leverage includes the Fund’s investments in the residual interest certificates (also called inverse floating rate securities) in tender option bond (TOB) trusts, including the portion of assets held by a TOB trust that has been effectively financed by the trust’s issuance of floating rate securities.
[24] Affiliated investment.
[25] The ratings disclosed are the lowest rating given by one of the following national rating agencies: Standard & Poor’s (S&P), Moody’s Investors Service, Inc. (Moody’s) or Fitch, Inc (Fitch). This treatment of split-rated securities may differ from that used for other purposes, such as for Fund investment policies. Credit ratings are subject to change. AAA, AA, A, and BBB are investment grade ratings; BB, B, CCC, CC, C and D are below-investment grade ratings. Holdings designated N/R are not rated by these national ratings agencies.
[26] Total investments include the Fund’s assets attributable to financial leverage. For these purposes, financial leverage includes the Fund’s investments in the residual interest certificates (also called inverse floating rate securities) in tender option bond (TOB) trusts, including the portion of assets held by a TOB trust that has been effectively financed by the trust’s issuance of floating rate securities.
[27] Affiliated investment.
[28] The ratings disclosed are the lowest rating given by one of the following national rating agencies: Standard & Poor’s (S&P), Moody’s Investors Service, Inc. (Moody’s) or Fitch, Inc (Fitch). This treatment of split-rated securities may differ from that used for other purposes, such as for Fund investment policies. Credit ratings are subject to change. AAA, AA, A, and BBB are investment grade ratings; BB, B, CCC, CC, C and D are below-investment grade ratings. Holdings designated N/R are not rated by these national ratings agencies.
[29] Total investments include the Fund’s assets attributable to financial leverage. For these purposes, financial leverage includes the Fund’s investments in the residual interest certificates (also called inverse floating rate securities) in tender option bond (TOB) trusts, including the portion of assets held by a TOB trust that has been effectively financed by the trust’s issuance of floating rate securities.
[30] Affiliated investment.
[31] The ratings disclosed are the lowest rating given by one of the following national rating agencies: Standard & Poor’s (S&P), Moody’s Investors Service, Inc. (Moody’s) or Fitch, Inc (Fitch). This treatment of split-rated securities may differ from that used for other purposes, such as for Fund investment policies. Credit ratings are subject to change. AAA, AA, A, and BBB are investment grade ratings; BB, B, CCC, CC, C and D are below-investment grade ratings. Holdings designated N/R are not rated by these national ratings agencies.
[32] Total investments include the Fund’s assets attributable to financial leverage. For these purposes, financial leverage includes the Fund’s investments in the residual interest certificates (also called inverse floating rate securities) in tender option bond (TOB) trusts, including the portion of assets held by a TOB trust that has been effectively financed by the trust’s issuance of floating rate securities.
[33] Affiliated investment.
[34] The ratings disclosed are the lowest rating given by one of the following national rating agencies: Standard & Poor’s (S&P), Moody’s Investors Service, Inc. (Moody’s) or Fitch, Inc (Fitch). This treatment of split-rated securities may differ from that used for other purposes, such as for Fund investment policies. Credit ratings are subject to change. AAA, AA, A, and BBB are investment grade ratings; BB, B, CCC, CC, C and D are below-investment grade ratings. Holdings designated N/R are not rated by these national ratings agencies.
[35] Total investments include the Fund’s assets attributable to financial leverage. For these purposes, financial leverage includes the Fund’s investments in the residual interest certificates (also called inverse floating rate securities) in tender option bond (TOB) trusts, including the portion of assets held by a TOB trust that has been effectively financed by the trust’s issuance of floating rate securities.
[36] Affiliated investment.
[37] The ratings disclosed are the lowest rating given by one of the following national rating agencies: Standard & Poor’s (S&P), Moody’s Investors Service, Inc. (Moody’s) or Fitch, Inc (Fitch). This treatment of split-rated securities may differ from that used for other purposes, such as for Fund investment policies. Credit ratings are subject to change. AAA, AA, A, and BBB are investment grade ratings; BB, B, CCC, CC, C and D are below-investment grade ratings. Holdings designated N/R are not rated by these national ratings agencies.
[38] Total investments include the Fund’s assets attributable to financial leverage. For these purposes, financial leverage includes the Fund’s investments in the residual interest certificates (also called inverse floating rate securities) in tender option bond (TOB) trusts, including the portion of assets held by a TOB trust that has been effectively financed by the trust’s issuance of floating rate securities.
[39] Affiliated investment.
[40] The ratings disclosed are the lowest rating given by one of the following national rating agencies: Standard & Poor’s (S&P), Moody’s Investors Service, Inc. (Moody’s) or Fitch, Inc (Fitch). This treatment of split-rated securities may differ from that used for other purposes, such as for Fund investment policies. Credit ratings are subject to change. AAA, AA, A, and BBB are investment grade ratings; BB, B, CCC, CC, C and D are below-investment grade ratings. Holdings designated N/R are not rated by these national ratings agencies.
[41] Total investments include the Fund’s assets attributable to financial leverage. For these purposes, financial leverage includes the Fund’s investments in the residual interest certificates (also called inverse floating rate securities) in tender option bond (TOB) trusts, including the portion of assets held by a TOB trust that has been effectively financed by the trust’s issuance of floating rate securities.
[42] Affiliated investment.
[43] The ratings disclosed are the lowest rating given by one of the following national rating agencies: Standard & Poor’s (S&P), Moody’s Investors Service, Inc. (Moody’s) or Fitch, Inc (Fitch). This treatment of split-rated securities may differ from that used for other purposes, such as for Fund investment policies. Credit ratings are subject to change. AAA, AA, A, and BBB are investment grade ratings; BB, B, CCC, CC, C and D are below-investment grade ratings. Holdings designated N/R are not rated by these national ratings agencies.
[44] Total investments include the Fund’s assets attributable to financial leverage. For these purposes, financial leverage includes the Fund’s investments in the residual interest certificates (also called inverse floating rate securities) in tender option bond (TOB) trusts, including the portion of assets held by a TOB trust that has been effectively financed by the trust’s issuance of floating rate securities.
[45] The ratings disclosed are the lowest rating given by one of the following national rating agencies: Standard & Poor’s (S&P), Moody’s Investors Service, Inc. (Moody’s) or Fitch, Inc (Fitch). This treatment of split-rated securities may differ from that used for other purposes, such as for Fund investment policies. Credit ratings are subject to change. AAA, AA, A, and BBB are investment grade ratings; BB, B, CCC, CC, C and D are below-investment grade ratings. Holdings designated N/R are not rated by these national ratings agencies.
[46] Total investments include the Fund’s assets attributable to financial leverage. For these purposes, financial leverage includes the Fund’s investments in the residual interest certificates (also called inverse floating rate securities) in tender option bond (TOB) trusts, including the portion of assets held by a TOB trust that has been effectively financed by the trust’s issuance of floating rate securities.
[47] The ratings disclosed are the lowest rating given by one of the following national rating agencies: Standard & Poor’s (S&P), Moody’s Investors Service, Inc. (Moody’s) or Fitch, Inc (Fitch). This treatment of split-rated securities may differ from that used for other purposes, such as for Fund investment policies. Credit ratings are subject to change. AAA, AA, A, and BBB are investment grade ratings; BB, B, CCC, CC, C and D are below-investment grade ratings. Holdings designated N/R are not rated by these national ratings agencies.
[48] Total investments include the Fund’s assets attributable to financial leverage. For these purposes, financial leverage includes the Fund’s investments in the residual interest certificates (also called inverse floating rate securities) in tender option bond (TOB) trusts, including the portion of assets held by a TOB trust that has been effectively financed by the trust’s issuance of floating rate securities.