The preferred style for Mission magazine is an em dash, surrounded by spaces. Example:
By some estimates, children are much more likely to miss school days due to dental-related problems than any other illness — a worry magnified in South Texas.
For number ranges and names of universities, use an en dash with no spaces. Example: 12–120.
On a Mac, the em dash is achieved through with this keystroke: shift + option + hyphen. The en dash uses this keystroke: option + hyphen.
On a PC, for an em dash: type 2014, then Alt + x. For an en dash: type 2013, then Alt + x.