A lot of countries have GQ Style, I was always surprised that the US didn't. I suppose they got burnt with Men's Vogue and decided to stay clear.
It comes out twice a year and generally has a much more 'directional' approach to the men's collections. I say 'directional', it's nothing cutting edge generally, it's usually just a little more like the main's magazine's more fashion-lead editorials and features. Along with more trend-lead grooming, styling etc. Well, that's how the British edition works anyway, I presume the US will follow the same suit.
It's still not as casual as Details was but it features more runway pieces and perhaps less suiting than the main magazine.