Detach debugger in Android Studio

In Android Studio, how do you detach the debugger once it's connected and debugging a running app?

In Eclipse, the icon looked like this .

I've been disconnecting the USB cable but that seems like a brute method.

The answer is the Close button. As of Android Studio v3.4 it's a red square block icon (previously was a red X).

It turns out I couldn't see it because it was hidden under the more >> icon.