Have they fixed the bug where IDEA runs so slow on 4k monitors that you can watch characters slowly appear after you've stopped typing? PLEASE FIX THIS WHY HAS IT NOT BEEN FIXED IN 2 YEARS?
I run IntelliJ IDEA (and AppCode and PyCharm and CLion and RubyMine) on an iMac 5K with a second 5K monitor attached, and on a Mac Pro with two 5K monitors attached. I've seen nothing like what you're describing.
This may not be a 4k issue. I had this issue when I first used the software on a sub-1080 monitor. I can't remember what fixed it but do make sure you have fast type mode enabled in your settings, or whatever they call it now.