How can I change the font size in the help viewer window?

I use a laptop with a very high resolution display and the help text in the right pane of the viewer is tiny, almost microscopic.
The TOC on the left pane looks OK.

How can I increase the text size of the right pane text?
Ctrl-mouse-wheel doesn't work, the window scrolls.
I have the latest IntelliJ Idea 15.0.1.