Flowering Shrub Identification Needed

Hello all - I recently moved to New York (near the border of Pennsylvania; about 2 hours northwest of NYC). I keep seeing these flowering shrubs growing wild along roadways, lakes, ponds, etc. Then I saw them planted near a mall along the highway as a privacy border. The multiple flowers are approx. 4-6 inches tall and grow straight up. They are blooming now (September). The plants grow 5-8 feet tall; looks like woody stems. Any idea what this is??

 

DOH! Eric is correct!
That's what I get for not clicking the image.

 

Looks like Fallopia japonica, Japanese knotweed.

 

That's it! Japanese Knotweed! Thank you!

 

An awful invasive weed - don't plant any!

 

Thank you to all who responded to my inquiry! Hearing how invasive this plant is, I don't think I should help to spread it -- especially in my own yard. Thanks again for your expertise!

 

Not a shrub. Foliage dies away each year.