an idealist - a) a person whose behaviour or thought is based on ideals; b) one who follows his ideals to the point of impracticality; a mere visionary or dreamer; c) an adherent or practitioner of idealism in art or philosophy.

idealism, the doctrine that a) truth, beauty and religious righteousness are more fundamental and useful than the external things in the world; b) things exist only as ideas in the mind rather than as material objects independent of the mind; c) things in the material world are actually manifestations of an independent realm of unchanging, immaterial models or forms.