Question has already been answered, but I will chime in only to say I wish the co-op servers were persistent for all players. In other words, the server owner did not have to be logged in for others to also log in. This is the reason I pretty much ONLY solo play now. I neither want to hinder others from potentially playing (by hosting) or be hindered from playing.

Of course, you can play any character on any server whenever you want so that's cool.