Dash convert to <del> tag

In my posts, I may have a negative number, say -90. If another dash comes later in the post, the dashes are replaced with the strikethrough tag. I’ve looked in functions-formatting and template-functions-post, but can’t seem to find where the conversion is happening.

Any tips? Thanks!

Oh … here’s an example:

http://www.warfarehq.com/page_left_column.php?content=article_disp&p=175&page=1

In the database, the <del>90</del> is -90-