Your game is using both the CPU and your graphics card. The 'idle' cycles that any BOINC client is using would be when your system in in idle - like when your screen blanks or goes to a screen saver.

If you're running a windows box, go into your task manager and click on the processes tab. If there's a button at the bottom that says something like "show processes from all users" click that. Now sort on the CPU column by clicking on it.

Now that you've done that, suspend BONIC and stop whatever else you may be doing on your machine. The top process in your task manager should now be the "system idle process". Those CPU cycles are what BOINC is using.

Hope that helps

Steve