How much is too much?

While I'm editing (and I edit often), I'm thinking; "I should add more there. Or should I?" So that's the big question for now. I could add more and then add more and so on and so forth. But how much is too much. I want those that read my book to be able to see it in their imagination my story but I also want some of it left for them to create in their own way. How many details is too much. The balance is an edgy thing.