Joshua 24 does not allege that Abraham was an idolater. It does state quite categorically that Terah was an idolater but if God wanted us to know that Abraham was an idolater, I think that somewhere in the hundreds of references about Abraham in the Bible it would have stated so. Was he a sinner. Yes. That is a fact. Was he an idolater? We don't know from scripture. I don't think we should smear Abraham with that sin unless it has been made clear in the scripture.