Tom Lehrer is one of the greatest satirists of all time. However, a recent decision by him also shows he has a gift for copyright.Tom Lehrer: The Public Domain Tango — Plagiarism Today.
Key points in the article. The article goes into more detail.
Note: It’s worth stating that the declaration deals with his compositions and his lyrics, not the recordings. Those are most likely not owned by Lehrer.
All the lyrics herein should be treated as though they were in the public domain.