How to set numwidth in the grid output of PL/SQL developer?

I'm running some queries in PL/SQL Developer, and one of the columns in the result has 18-digit numbers. Instead of displaying the entire number in the resulting grid, PL/SQL Developer displays only 15 digits in scientific notation.

I tried to find a way to change this in the preferences of the program, so that I'll see the entire number, just like set numwidth does in SQL*Plus. But my search was futile.

How do I change this setting?