It's a perennial, not an annual. Not necessary to bring inside to keep it going, although you can keep it growing as a houseplant. However, if you do keep it outside, and plant it in the ground, know that it can become quite aggressive and get into places you don't want it.
Thank you for replying. I can't plant them because I am in an apartment but they are growing great as hanging baskets. I didn't want to get rid of them at the end of the season if I can bring them in as a houseplant for the winter and then return them back outside next spring/summer.
Give it a try. They might look a little tattered after the winter, but if they do, give them a haircut and a dose of fertilizer, and they'll probably come back better than ever.