So the literal translation is "for other one decade". I do think "for over a decade" does not mean "for another decade". It should mean "for the whole ten years and more" responding to questions like "how long have you been here?"
FRA is wrong in the context.
The phrase you wrote means "in over a decade", meaning something will happen after the decade is over.
"PER più di un decennio" means that something is happening or happened for more than a decade, not after.
Drat, was proud of myself to get the 'Per oltre' but marked incorrect for double consonant in wrong place 'decennio' not 'deccenio'! I'm usually pretty good at checking spelling by phonics but this C=ch sound didn't register in my writing sigh