Strategy. To pursue its goal, the fund normally invests at least 80% of its net assets, plus any borrowings for investment purposes, in municipal bonds that provide income exempt from federal personal income tax. Typically, the fund invests substantially all of its assets in such municipal bonds. Municipal bonds are debt securities or other obligations issued by states, territories and possessions of the United States and the District of Columbia and their political subdivisions, agencies and instrumentalities, or multistate agencies and authorities. The fund invests at least 70% of its net assets in municipal bonds rated, at the time of purchase, investment grade (i.e., Baa/BBB or higher) or the unrated equivalent as determined by Insight North America LLC, the fund's sub-adviser. … Show more… To pursue its goal, the fund normally invests at least 80% of its net assets, plus any borrowings for investment purposes, in municipal bonds that provide income exempt from federal personal income tax. Typically, the fund invests substantially all of its assets in such municipal bonds. Municipal bonds are debt securities or other obligations issued by states, territories and possessions of the United States and the District of Columbia and their political subdivisions, agencies and instrumentalities, or multistate agencies and authorities. The fund invests at least 70% of its net assets in municipal bonds rated, at the time of purchase, investment grade (i.e., Baa/BBB or higher) or the unrated equivalent as determined by Insight North America LLC, the fund's sub-adviser. For additional yield, the fund may invest up to 30% of its net assets in municipal bonds rated, at the time of purchase, below investment grade ("high yield" or "junk" bonds) or the unrated equivalent as determined by the fund's sub-adviser. The dollar-weighted average maturity of the fund's portfolio normally exceeds ten years, but the fund may invest without regard to maturity or duration. A bond's maturity is the length of time until the principal must be fully repaid with interest. Dollar-weighted average maturity is an average of the stated maturities of the bonds held by the fund, based on their dollar-weighted proportions in the fund. Duration is an indication of an investment's "interest rate risk," or how sensitive a bond or the fund's portfolio may be to changes in interest rates. The fund's sub-adviser focuses on identifying undervalued sectors and securities. To select municipal bonds for the fund, the sub-adviser uses fundamental credit analysis to estimate the relative value and attractiveness of various sectors and securities and actively trades among various sectors and securities based on their apparent relative values. The fund seeks to invest in several different sectors, and does not seek to overweight any particular sector but may do so depending on each sector's relative value at a given time. A rigorous sell discipline is employed to continuously evaluate all fund holdings. Current holdings may become sell candidates if creditworthiness is deteriorating, if bonds with better risk and return characteristics become available, or if the holding no longer meets the sub-adviser's strategic or portfolio construction objectives. Although the fund seeks to provide income exempt from federal income tax, income from some of the fund's holdings may be subject to the federal alternative minimum tax. Show less