Convert 20121004 (yyyyMMdd) to a valid date time?

Question

I have a string in the following format yyyyMMdd and I am trying to get it to look like this:

yyyy-MM-dd

When I try:

Answer 1

It's a little ugly, but how about this?

date.Insert(6, "-").Insert(4, "-");

If you can assume you're coming in with a string representing a valid date and you don't need to do any other date-ish logic, then why go to a DateTime in the first place?