In an article about who owns an idea The New York Times quotes Professor Lawrence Lessig:

When disputes over the provenance of an idea become particularly turbid, disappointed entrepreneurs will look to the courts, which often are of little help. As Lawrence Lessig, a professor at Stanford Law School, said, “The general rule is that ideas are free unless strapped down by contract or patent.” In practice, a great idea is owned by whoever expresses that idea most successfully.