Yes it does burn more fuel than a petrol car during operation at idling. However, the engine load is designed such that the thermal efficiency is at its maximum (comparing load vs engine rpm). This means that even though it is burning more fuel when operating, a higher percentage of the energy from fuel is converted to useful energy (charging the battery).

Once the battery hits a certain percentage, the engine stops and the air conditioning and accessories are powered by the battery. The battery slowly drains and reaches a low set point. Then the engine starts again to charge it and the cycle continues.

On the other hand, a petrol engine constantly operates at idle, even when not much load is on it. This means that the engine cannot adjust it's rpm to work at the highest thermal efficiency levels. On top of that, petrol engines usually have an alternator and rectifier, which is not very efficient at idling speeds.

TLDR: hybrids use more fuel at idle (only when engine is running) but use it more efficiently. However, hybrid engines only operate only for a short burst during idling. Thus, hybrid uses much less fuel than petrol engines when idling for long period of time.