What is the tall art deco building bordering Washington Square Park?

If you are standing near the fountain in the middle of Washington Square Park in Manhattan, and you look to the northeast, there is a very prominent art-deco style building. I don't think it actually borders the park, but it comes close. It looks a bit odd near the top because it becomes very thin at the top few stories, and it appears to be made of brownish concrete. What is the name of this building? What is its purpose?