I have a 1991 quarter P mint mark that has no reeding and is slightly thicker than a standard quarter. I am not sure if it was pressed incorrectly or if this is was done after the mint. I have looked under a loop and I can't see any doubling like it was stamped twice. Both sides you can feel a lip all the way around the edges.
kylekeen, to the forum, first post! Nice pics, by the way, thank you for that, it helps greatly.
It could be as Spencer said, a dryer coin but would suspect it is a coin that has been in a bezel or encased. When it's a dryer coin, the devices are usually enlarged also, which I don't see. With the extreme difference in the rim thickness, it would show enlarged devices, if it were a dryer coin, in my opinion. Regardless, it is damage and worth a quarter.