Water And Sewer Revenue Bonds [Member] C000074146 [Member] Institutional Class C000006387 [Member] Class C C000006385 [Member] Class A WISCONSIN ARIZONA PUERTO RICO ALABAMA CALIFORNIA COLORADO FLORIDA ILLINOIS NEW JERSEY NEW YORK PENNSYLVANIA TEXAS C000006388 [Member] C000006390 [Member] C000074147 [Member] Bloomberg Municipal Bond Index [Member] Bloomberg 3 15 Year Blend Municipal Bond Index [Member] Industrial Development Revenue Pollution Control Revenue Bonds [Member] Special Tax Revenue Bonds [Member] Transportation Revenue Bonds [Member] Healthcare Revenue Bonds [Member] Education Revenue Bonds [Member] Lease Revenue Bonds [Member] State General Obligation Bonds [Member] Housing Revenue Bonds [Member] Electric Revenue Bonds [Member] Local General Obligation Bonds [Member] Investment Type [Axis] Net Assets Investment Company Portfolio Turnover No Trading Symbol Flag