2017.2 and before I never had scaling issues. The 2017.3 update made every UI element just really big, except for the editor fonts. Icons, menu items, etc. are all big. This also affects the loading splash on first start - it is noticeably larger than the 2017.2 splash was. I haven't noticed these issues on my other machines.
Here's IDE and system information:
IntelliJ IDEA 2017.3.1 (Ultimate Edition)
Build #IU-173.3942.27, built on December 11, 2017
Licensed to Minecraft Development for IntelliJ / Kyle Wood
Subscription is active until August 30, 2018
For non-commercial open source development only.
JRE: 1.8.0_152-release-1024-b8 amd64
JVM: OpenJDK 64-Bit Server VM by JetBrains s.r.o
And a screenshot: