When the cabin descent time is longer than aircraft descent time the initial rate of aircraft descent needs to be less than obtained at idle thrust till both meet at same point on ground. This is known as repressurization segment. During this phase in A330 FMA shows as THR DES which higher than idle and then it comes back to THR IDLE. Even idle thrust value is subject to bleed demand as anti ice etc. and is called modulated idle. Same thing happens in A320 but FMA shows only THR IDLE.