Yeah, Turgon wasn't into the whole incest thing. Regarding Idril, he told Maeglin, they were "too close of kin."

On the other hand, I think there were marriages like that in the other elvish households. Maybe. Can't really remember. I know Aragorn and Arwen are related.

Yeah, but we're talking great, great, greatgreatgreatgreatgreatgreat cousin. That might be a titch different.

True. I'd have to look if there were any other instances.