This detail supports the central idea that riches are not important to utopians. it is best described as a(n) fact. analogy. anecdote. example.

It is described as anecdote. Anecdote is a brief, revealing account of a person or an incident, normally they differ from jokes because their primary purpose is to reveal a truth and not simply to provoke laughter. It serves to make listeners laugh or ponder over a given topic, it relates to the subject matter being discussed by a group of people. 

The fact that farmers were paid for destroying crops.