Once you register to vote, are you always registered?

This might be a stupid question, but I am curious. I registered to vote when I turned 18, and never voted. (I am now 20). Since I registered then, am I always registered? Also, if I move, do I have to re-register?

I live in Idaho if that matters.
Update: BAH! I got married... I didn't even think about me changing my name.
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