Mating: an idea gone over repeatedly (4,3,5)

I believe the answer is:

time and again

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'repeatedly' is the definition.
(I've seen this before)

'mating an idea gone' is the wordplay.
'mating an idea' anagrams to 'TIME AND AGAIN'.
Though, I'm not clear how this is indicated.

'over' acts as a link.

Can you help me to learn more?

(Other definitions for time and again that I've seen before include "Repeatedly" , "frequently" .)

I've seen this clue in The Sunday Times and The Times.

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