There are 6 picas per inch, 12 points per pica, and thus 72 points per inch. 1/8" is 9 points or 1.5 picas. Clear as mud?
Clear as mud! I think I need another cup of coffee Any ideas on how to enlarge the brochure 1.5 picas on all sides?
It sounds like you printer wants you to add bleed to your file.
You can leave the page size as is, and add the bleed (1p6) in the document setup.
Then, making sure you are not in preview mode, show guides.
Pull your doument elements out to the red guides outside the page area.
If you are sending a pdf to the printer, be sure to include marks and bleeds in the output.
Just add bleed 1/8 inch
Then export to PDF
But - after working in prepress from 2001 to 2006 - enlarging documents by 1/8 inch was pretty normal.
Shame your print provider can't do this.
What version of InDesign are you using? Prior to InDesign CS5, the best way is to use File > Document Setup.
I've found best results in CS5 and later to use the Page tool.
Here is your original page: 51p x 66p, with Page tool selected:
Set the reference to point to the center, and change the dimensions to 52p6 x 67p6 [that means 67 picas and 6 points].