This depends a great deal on the individual person. Also, idealism and truth may well have different levels of significance for a given person.
For me, the only place where idealism really comes into play is in my dealings with my family. I am absolutely idealistic when dealing with my wife and kids. What I mean by that is that I try to do what I think is right, not what I think is convenient.
As for truth, I do value telling the truth in all important things. I do not really think that it is important to tell the absolute truth all the time, but I do think you should always tell the truth to important people on important subjects.