You’ll have to experiment a couple different ways since you’re using a wide logo. You can try adding
background-size: contain !important; to your #header (around line 2803 in the blue section or wherever you want) and that would sort of resize it when you adjust your browser. Give that a try first.
I would recommend using a smaller version of the logo when accessed by a mobile device/browser because the logo you have will probably be too small to see.
If you haven’t already, check out this tutorial – http://www.carriedils.com/add-logo-genesis-theme/ it just covers some of the basics (you may already know this).