Bloomberg Municipal Bond 7 Year Index [Member] Bloomberg U S Municipal Bond Index [Member] TEXAS UTAH VIRGINIA WASHINGTON WISCONSIN GEORGIA ILLINOIS INDIANA IOWA LOUISIANA MASSACHUSETTS MICHIGAN NEW HAMPSHIRE NEW JERSEY NEW YORK NORTH CAROLINA OHIO OREGON PENNSYLVANIA SOUTH CAROLINA TENNESSEE ALABAMA ARIZONA CALIFORNIA COLORADO CONNECTICUT FLORIDA Transportation Sector [Member] Education [Member] Housing [Member] Development [Member] Tobacco Settlement [Member] School District [Member] Power [Member] Nursing Homes [Member] Water And Sewar [Member] Medical [Member] Airport [Member] Student Loan [Member] General Obligation [Member] Net Other Assets and Liabilities [Member] Net Other Assets and Liabilities Country [Member] C000000110 [Member] Composite Class Investment Type [Axis] Net Assets Investment Company Portfolio Turnover No Trading Symbol Flag