Why is Garmin, Ltd. (GRMN) down nearly 20% in the past 2 months?

I read that the most recent earnings were not as impressive, although they beat expectations, and that the guidance is a bit weak for this holiday season. They’ve also got some competition in wearables market from Apple, Fitbit, and Amazon.

They’ve had a decent run up this past year, but 20% drop seems a bit much. Any thoughts on this?