Weed ID, please?

[sherrold]

It's pretty, but I know I didn't plant it, and in a year it's spread to four different beds. Sadly, neither of these are great pictures, either. It has an upright pattern, reaching 3-4 ft., with small pine-needle-like leaves all up and down its stalks. The flowers are purple, or pink, or white.







I've let them grow because the bees love them, and they're pretty. But if they're as invasive as I suspect, I bet it's my obligation as a citizen to pull them out.

Any ideas?