What do you mean by idealist? Plato is considered an idealist because he believed in a realm of ideas or forms that everything in the world was a reflection of. Thomas was more of an aristotealian and consequently a realist because he believed the forms were in the object. The soul is the form of man, and the body is the matter.
The modern meaning of idealist is a little different though.
Also, what does it mean to be a thomist? What is the limit on how much you have to agree with Thomas? An idealist certainly wouldn’t be a thomist on the questions of anthropology and cosmology.