If you are basing it off of something you would not have learned unless it was on that job it would not likely be yours. For a concept to be yours, it must be one you could have thought of without having had any connection to that company or use of its assets.
If it was something that occurred to you while on the premises but not specifically inspired by something only available to you at THAT job (and you have not contributed it to that job/left any record of your thoughts about it on the job) then in my opinion, it's as if you created it without them. I'm not a lawyer, but here's my logic.
Example: I am a cookie baker hired to work at a baking company coming up with secret recipes for chocolate chip cookies. One day, I thought that adding guacamole would really enchance the flavour. If I don't tell anyone at the company about it, there's no guacamole at the job site that is being considered as an ingredient, and I go home and experiment with guacamole to discover it's the best recipe idea ever, it would be my idea.
Chocolate chip cookies are not the sole domain of that company, there was nothing at the company which inspired my idea, and the idea could have as easily come to me at home in my own kitchen while baking my own cookies. Companies do not own thoughts that occur while on the premises, if those ideas are not inspired by something on the premises.
Now if it was someone else's idea to add guacamole to those cookies, and all you did was figure out an amount to add that tasted better, then it is based on information already owned by the company, you would be out in the cold.